Charts Definition Language (CDL): Difference between revisions

Revision as of 14:27, 6 January 2024

Introduction

The Charts Definition Language gives the user the possibility to define his own charts on the basis of the CumulusMX infrastructure through the ChartsCompiler. This article gives the specification of that language.

CutilsCharts.def

The charts are defined in the definition file (CutilsCharts.def which resides in the utils directory) which contains one or more chart specifications according to the figure below. All attributes of a plot variable are optional and if not specified have a reasonable default. All white space characters are used as separators so it is easy to make a visually attractive, readable definition file.

The text in the CutilsCharts.def is case independent, however for clarity CamelCase or a variety thereof is advised.

The ChartsCompiler is obligatory after the introduction of the ExtraSensors module from version 6.5 onwards where the ChartsCompiler is used internally for defining and creating the charts for the ExtraSensors module which would otherwise - in a generic way - be virtually impossible. The CutilsCharts.def has a demarcation line which separates the Extra Sensors Charts (below) from the user charts (above). The user may want to create his own Extra Sensor Charts and he can do so by setting the parameter UserModificationExtraSensorCharts=true, if he does so existing Extra Sensors charts in the CutilsCharts.def file remain untouched.

A standard CutilsCharts.def and a CutilsCharts-example.def can be found in the distribution. The first for an initial minimum setup, the second to guide the user into the possibilities.

The specification

Chart Compiler Language (CDL) specification

The Language

The Chart block

 CHART <id> TITLE [<word>...<word>]  
   CONNECTSto [1 … 24]
   HAS WINDBARBS [ ABOVE | BELOW ]
   ZOOM <Integer>

   [ PLOT [ALL||DAILY|RECENT|EXTRA] <Plotvariable> [ EVAL '[' <Expression> ']' ]  ] 
 | [ STATS [ALL||DAILY|RECENT|EXTRA] <Plotvariable> <Stats Type> ]
            AS <Line Type> 
            COLOUR <HTML Color>
            ZINDEX <Integer>
            LINEWIDTH <Integer>
            OPACITY <Integer>.<Integer>
            AXIS <Axis Type>
            INVISIBLE

 PLOT blocks repeated
 STATS blocks repeated
   [...]

 ENDCHART 
 OUTPUT <filespec>
 INFO " <free text> "

 CHART […] ENDCHART blocks repeated

Plot blocks can be repeated as many times as you wish but different parameters can result in many yAxis (making the plot area smaller) and the chart may become crowded and unreadable. Experiment and try-out.

Syntactically the STATS block can be many as well but it requires semantically the Plotvariable of which you want statistics to be plotted normally. So you can have e.g. three STATS blocks for one PLOT block.

Output specifier

An output file can be specified for each chart by putting OUTPUT <filename> after an ENDCHART. All charts from that point on will be written to that specified output until a new output is specified for another chart. If no output is specified at all, all charts will be written to cumuluscharts.txt (the default output)

If you are using the website it is important to know that the first chart will always be used as the chart for the Home page button and that cannot be changed (the file is always cumuluscharts.txt). If, however you specify an output on the first chart, that chart will be duplicated in the output you specify.

The output specifier gives the user the possibility to define charts as he likes and to place these in the menu wherever he likes. In the Website Generator the placements of the charts at the moment will be limited to the User Defined Menu. In modular use the user can do whatever he likes with the resulting files. In the website the charts require the datafiles to be in the current directory.

Info specifier

A free helptext can be specified after the chart using this keyword:

 INFO " This is a free HTMLformat helptext which can contain an axplanation of the chart "

The double quotes around the helptext are obligatory and must be enclosed by spaces.

Keywords

All capital written words in the Chart block section are keywords (reserved words) and have meaning.

Explanation of the definition Keywords

EQUATIONS (Optional construct): Starts an equations block. Such block only defines (partial) equations, it does not cause code generation in itself
CHART: Starts a chart definition
TITLE: Starts the title. All words until the next keyword comprise the title of the chart
CONNECTSTO (Optional construct): The integer numbers which follow CONNECTSTO represent a pane in the realtime dashboard. When clicked on that pane this chart appears. This is only valid on charts in the default output. For other outputs there is no semantics for CONNECTSTO and a warning is issued in the logfile if it is specified in any second or higher output.
HAS WINDBARBS [ ABOVE | BELOW ] (Optional construct): Defines if the chart displays the WINDBARBS showing direction and speed as indicators (this is not an exact plot of wind). Above | Below specifies the place in the chart.
ZOOM (Optional construct): Indicates which range selector button is the default when the chart is displayed; Defaults depend on chart range.
PLOT: Starts the plot specification using one of the possible variables. Each chart requires at least one PLOT.
STATS: Starts the statistics block using one of the possible variables. Semantics demands the variable to be plotted normally as well.
RECENT: Defines the variable to be governed by the CMX parameter GraphHours and are similar to the CMX RECENT graphs (though not equal).
ALL: Defines the variable to be taken from the Dayfile and all data for that variable will be plotted (Note that the CMX parameter ChartMaxDays will not be used)
DAILY: Identical to the ALL keyword but it sets the datarange for the chart to one month while the ALL keyword sets it to one year.
EXTRA: Defines the variable to be an extra sensor variable. It has an implicit datarange of RECENT.
AS (Optional construct): Defines the type of charting for that variable. All attributes of AS are optional.
EVAL [ ]: Defines an expression for the plot variable. The equation must be placed between the square brackets, space has no value here (does not act as separator).
COLOUR: Defines the colour of that variable.
ZINDEX: Defines the zIndex plane for that variable.
LINEWIDTH: Defines the linewidth for that variable. When the chart type is scatter, this attribute defines the radius of the points.
OPACITY: Defines the opacity for that variable (important for area and column graphs)
AXIS: Gives the user the possibility to specify an axis when using the EVAL construct otherwise an error is generated.
INVISIBLE: Gives the user the possibility to switch off the initial display of a series.
ENDCHART: End the chart definition
OUTPUT (Optional construct): Gives an optional name of an outputfile which starts at the chart where it is defined. Any chart after this OUTPUT specifier goes to this OUTPUT until another OUTPUT is found. Only the first OUTPUT specifier (implicitly: cumuluscharts.txt) accepts click events as defined by CONNECTSTO.
INFO (Optional construct): Introduces a helptext section for the chart. The free text is enclosed in double quotes and cannot contain double quotes. The double quotes are delimited by a space character.

The keywords for the actual parameters and the Graph Types speak for themselves.

Plotvariables

The following PlotVariables are reserved words:

With the RECENT qualifier

     "InsideTemp", "Dewpoint", "ApparentTemp", "FeelsLike", "WindChill", "HeatIndex","Temperature", "Humidex",
     "WindGust", "WindSpeed",
     "Bearing", "AverageBearing",
     "UV", "CurrentSolarRad", "TheoreticalSolarMax",
     "RainFall", "RainRate",
     "Pressure",
     "Humidity", "InsideHumidity",
     "EvapoTranspiration"

NOTE: The RECENT qualifier is optional as it is the default for a chart.
NOTE: The zoom buttons for the RECENT chart $1/4$ and $1/2$ the value of the hours specified in the CMX parameter GraphHours.

With the ALL/DAILY qualifier

     "MinTemp", "MaxTemp", "AverageTemp", "AvgWindChill", "MaxDewpoint", "MinDewpoint","MaxFeelsLike", "MinFeelsLike", 
     "MaxGust", "WindRun", "HighAvgWindSpeed", 
     "UV-Index", "SolarRadiation", "SunHours",
     "DayRain", "MaxRainRate",
     "MinBarometer", "MaxBarometer",
     "MinHumidity", "MaxHumidity",
     "HeatingDegreeDays","CoolingDegreeDays","DayEVT"

Note: The difference between ALL and DAILY is only between the displayed datarange (6 months or 1 month)

With the EXTRA qualifier

     "Temp1","Temp2","Temp3","Temp4","Temp5","Temp6","Temp7","Temp8","Temp9","Temp10",
     "Humidity1","Humidity2","Humidity3","Humidity4","Humidity5","Humidity6","Humidity7","Humidity8","Humidity9","Humidity10",
     "Dewpoint1","Dewpoint2","Dewpoint3","Dewpoint4","Dewpoint5","Dewpoint6","Dewpoint7","Dewpoint8","Dewpoint9","Dewpoint10",
     "SoilTemp1","SoilTemp2","SoilTemp3","SoilTemp4","SoilTemp5","SoilTemp6","SoilTemp7","SoilTemp8","SoilTemp9","SoilTemp10",
         "SoilTemp11","SoilTemp12","SoilTemp13","SoilTemp14","SoilTemp15","SoilTemp16",
     "SoilMoisture1","SoilMoisture2","SoilMoisture3","SoilMoisture4","SoilMoisture5","SoilMoisture6","SoilMoisture7","SoilMoisture8","SoilMoisture9","SoilMoisture10",
         "SoilMoisture11","SoilMoisture12","SoilMoisture13","SoilMoisture14","SoilMoisture15","SoilMoisture16",
     "AirQuality1","AirQuality2","AirQuality3","AirQuality4",
     "AirQualityAvg1","AirQualityAvg2","AirQualityAvg3","AirQualityAvg4",
     "UserTemp1","UserTemp2","UserTemp3","UserTemp4","UserTemp5","UserTemp6","UserTemp7","UserTemp8",
     "LeafTemp1","LeafTemp2","LeafWetness1","LeafWetness2",
     "CO2", "CO2_24h", "CO2_pm2p5", "CO2_pm2p5_24h","CO2_pm10","CO2_pm10_24h","CO2_temp","CO2_hum"

Note: The EXTRA qualifier indicates plotvariables for the Extra Sensors. These are implicit RECENT but come from a different source.

Types

Graph Types

The following graphs are possible

     Line, SpLine, Area, Scatter, Column, ColumnRange

All graph types can be combined in a chart except for Scatter.

ColumnRange only works for DAILY and ALL range specifiers. If the Max and Min lines of the range must be shown, they need to be specified as a separate line. The range can be specified for either Min or Max, the range will automatically be applied and no line will be shown. The ColumnRange is valid for all variables in the datafile with a Max/Min range: Temperature, Dewpoint, FeelsLike (and other derivatives), Barometer and Humidity. Other variables will generate an error.

Axis Types

The following Axis are possible.

     Temp, Wind, Distance, Height, Hours, Solar, UV, Rain, Rrate, Pressure, Humidity, DegreeDays, EVT, AQ, ppm, Free

This only has meaning if there is an EVAL with a valid expression present. As an EVAL may modify the value of the plot variable to something completely different, the original Axis belonging to that plot variable may be useless or scale wrongly. Therefore you can choose your own Axis. If there is no valid equation, a warning is given and no axis is generated.

A generic (without title or unit) Axis is selectable to accommodate plotting in combination with other variables, this is the Free axis type.

Other Types

For other types such as STATS types (or methods) and FUNCTION types for EVAL, see those respective pages for STATS and for EVAL.

Equations

See page CDL - EVAL.

The Chart Axis

All PlotVariables have their own defined axis and those axis will be coupled automatically to the chart. Multiple axis will be alternately added left-right where the order in the definition files determines this order. So it is the user who ultimately can define where the axis are placed: left or right and from inside to the outside in the order where they are encountered during the parsing process.

The scaling of the axis is flexible i.e. it starts with a reasonable value for the upper and lower bounds and adjusts if the real values are higher or lower. For some axis the lower bound is always 0 (e.g. rain) for another the upper and lower bounds are fixed. Specifics are found below.

The following axis are currently defined and implicit for the plot variables (the user has no options here):

None
Temp - automatic scaling for min/max
Pressure - scaling with a pseudo-fixed scale which means the min/max values of the scale are set to the min/max all time records found in alltime.ini. Highcharts itself sets the scale values such that there is a tick at the end of the scale and the min/max values fall between the ticks at the end of the scale. If the pressure gets a lower/higher value the axis will adjust automatically. The idea is that any barometer you have at home has a fixed scale and with small variations there is little movement of the needle. However when the pressure starts falling/rising significantly it is very obvious. This behaviour is mimicked by CUtils (as far as possible)
Rain - automatic scaling with minimum value of 0 and an initial maximum of 1 (to accommodate measurement in inches)
Rrate - automatic scaling with minimum value of 0 and an initial maximum of 1 (to accommodate measurement in inches)
Wind - automatic scaling for min/max
Direction - scaling is fixed for 0 to 360 degree. When only direction is plotted two axis are created: in degrees and in wind directions (N, E, S, W). When combined with another unit only the axis with wind directions is used.
Humidity - scaling is fixed between 0 and 100
Solar - scaling is fixed between 0 and a rough estimate of the maximum theoretical value for radiation + 50 to give the scale some space. If the actual value goes beyond that, the scale will adjust.
UV - automatic scaling for maximum, minimum is 0
Hours - automatic scaling for maximum, minimum is 0
Distance - automatic scaling for maximum, minimum is 0
Height - automatic scaling for maximum, minimum is 0, basically used for the Cloudbase
DegreeDays - automatic scaling for maximum, minimum is 0
EVT - automatic scaling for maximum, minimum is 0
Free - has no title, unit or context associated with it. It just displays values. Automatic scaling for min/max.
AQ - automatic scaling for maximum, minimum is 0
ppm - automatic scaling for maximum which starts at 500, minimum is 0. The default maximum is because the CO₂ value is around 420 (in 2022) outdoors.

Translations for the axis titles come from the [Website] section (until EVT) and should require no additional effort. Subsequent translations of axis titles come from the [Compiler] section (from Free onwards) and may require translation.

Additional details

All parameters can be combined in one graph with the corresponding axis automatically added. ~~Only when scatter is defined as Line Type it is forbidden to combine it with one of the other possibilities. This may change in future.~~ The scatter combination with other charts types is now available but may be subject to change.
The Legend texts are implemented as translations of the PlotKeywords (the Plot Variables). You will find these in the translation file section [Compiler]. Legend entries can be multiple words (the keywords can not).
The width of the graph container is 100% of the viewport.
The height of the graph container can be specified in the inifile parameters (not defined in the language to prevent overcharge):

 [General]
 ChartContainerHeight=650 (Default)

The Plot Variables Evapotranspiration, CoolingDegreeDays and Heating DegreeDays are not supplied by CMX in the JSONs. CumulusUtils provides those automatically when used in the definitions (on request) with the commandline parameter UserAskedData.
All Extra Sensor Plotvariables are supplied by CumulusUtils through the commandline parameter UserAskedData.
For the commandline parameter UserAskedData: see also ChartsCompiler Operation.
You have to schedule UserAskedData command if you wish to use the FTP frequency CMX uses for its JSON's. Note that these JSON files specific to CumulusUtils always reside in the website root of CumulusUtils, even if you have more websites and define the CumulusRealTimeLocation.
If the user uses different locales for CMX and CumulusUtils the monthly log filenames will be according to the locale of CMX. This creates an issue which is solved by the inifile parameter:

 [General]
 MonthsOfMiracleAndWonder=jan,feb,mrt,apr,mei,jun,jul,aug,sep,okt,nov,dec

Default this variable contains the abbreviated month names according to the locale of CumulusUtils. The user may edit those names to the ones used by CMX if CMX uses another locale than CumulusUtils which creates conflicts in the names the monthly log files.

Example CutilsCharts.def

The Chart definitions below is included in the distribution of CumulusUtils and serves as an example.

;
; ChartsCompiler Demo and test chart definitions - Part of CumulusUtils
;
; © Copyright 2019 - 2021 Hans Rottier <hans.rottier@gmail.com>
;
; 
; Author:      Hans Rottier <hans.rottier@gmail.com>
; Project:     CumulusUtils meteo-wagenborgen.nl
; Date:        04-08-2021
;

Equations
; Water Vapour Saturation Pressure according to the August-Roche-Magnus equation for the 1980 version, the 2008 version and the sub-zero version
  Psat2008 EVAL [ 6.112 * EXP(17.62*Temperature/(243.12+Temperature)) ]
  Psat2008ALL EVAL [ 6.112 * EXP(17.62*AverageTemp/(243.12+AverageTemp)) ]
  Psat1980 EVAL [ 6.1094 * EXP(17.625*Temperature/(243.04+Temperature)) ]
  PsatSub0 EVAL [ 6.112 * EXP(22.46*Temperature/(272.62+Temperature)) ]

; Actual Vapour Pressure
  Avp Eval [ Humidity / 100 * Psat2008 ]

; Humidex as in CMX
  CDLHumidex Eval [ (Temperature + 5.0 / 9.0 * (Psat2008 - 10.0)) ]

; Do the WindChill According to https://sciencing.com/relative-humidity-7611453.html / CMX
; Note: the eqn is only valid for degr Celsius and Kmh.
; See https://sciencing.com/relative-humidity-7611453.html for imperial formula.
;  WindPOW Eval [ pow(WindSpeed, 0.16) ]
;  CDLWindChill Eval [ 13.12 + 0.6215 * Temperature - 11.37 * WindPOW + 0.3965 * Temperature * WindPOW ] 

; Apparent Temperature as in CMX (WindSpeed in ms so convert to Kmh, divide by 3.6
  AppTemp Eval [ Temperature + 0.33 * Avp - 0.7 * WindSpeed / 3.6 - 4.0 ]

; WetbulbTemperature in degr Celsius
  WetBulbTemp Eval [ 0.00066 * Pressure * Temperature + 4098 * Psat2008 / (Pow( Dewpoint + 237.7, 2) * Dewpoint) / (0.00066 * Pressure + 4098 * Psat2008 / Pow(Dewpoint + 237.7, 2)) ]


Chart Overzicht Title Overzicht van de huidige weerstatus ConnectsTo 2 4 15 20
Has WindBarbs Above
  PLOT Temperature Colour #058DC7 zindex 90
  PLOT DewPoint Colour #50B432 zindex 80
  PLOT pressure Colour red zindex 70
  Plot Humidity Colour #64E572 zindex 60
  Plot SolarRadiation As Area Opacity 0.2 Colour Orange zindex 20
  Plot RainFall As Area colour #33B4FF opacity 0.2 zindex 10
EndChart

Chart Temperatuur Title Temperatuur en afgeleiden ConnectsTo 1 13 14
  Plot InsideTemp As Spline Colour #DDDF00 zIndex 100
  PLOT Temperature As SPline Colour #058DC7 zindex 90
  PLOT FeelsLike As SPline Colour #ED561B zindex 80
  PLOT DewPoint As SPline Colour #50B432 zindex 70
EndCHART

Chart Wind Title Wind ConnectsTo 5 8
  Plot WindGust
  Plot WindSpeed
EndCHART

Chart Windrichting Title Windrichting ConnectsTo 6 7 
  Plot Bearing As Scatter
  Plot AverageBearing As Scatter
EndCHART

Chart Regen Title Regen and Regensnelheid ConnectsTo 3 21 22
  Plot RainFall As Area Colour green Opacity 0.2
  Plot RainRate zIndex 100
EndChart

Chart Vochtigheid Title Relatieve vochtigheid binnen en buiten ConnectsTo 11 16
  Plot Humidity
  Plot InsideHumidity
EndChart

Chart Zon Title (Max)Straling en UV ConnectsTo 12 23 24
  Plot  UV  zIndex 100
  Plot  SolarRadiation As Area Opacity 0.4 Colour Orange zIndex 50 
  Plot  TheoreticalSolarMax As Area Colour Gold zIndex 10 Opacity 0.2
EndChart

CHART DagelijkseTemp TITLE Dagelijkse gem. temperatuur met columnrange
  PLOT DAILY AverageTemp colour green As ColumnRange
  PLOT DAILY AverageTemp colour black As spline
EndChart

CHART DagelijkseBaro TITLE Dagelijkse gem. barometer met columnrange
  PLOT DAILY MinBarometer colour Crimson As ColumnRange
  PLOT DAILY AverageBarometer EVAL [ (MinBarometer + MaxBarometer)/2 ] colour black As spline Axis Pressure
EndChart

CHART DagTemp TITLE Dagelijkse Gemiddelde Temperatuur met Min/Max van afgelopen jaar
  PLOT DAILY AverageTemp colour green
  Plot DAILY MinTemp colour blue
  Plot DAILY MaxTemp colour red
EndChart OUTPUT AllChart.txt

Chart DagRegen Title Dagelijkse regenval van afgelopen jaar
  Plot DAILY RainFall As Column colour lightblue
EndChart 

Chart DagZonuren Title Zonuren per dag van afgelopen jaar
  Plot ALL SunHours As Column colour gold
EndChart 

Chart TempEVT Title Temperatuur en EVT - Historische Data ConnectsTo 12 23 24
  PLOT ALL AverageTemp As SPline Colour #058DC7 zindex 90 LineWidth 10
  PLOT ALL Evapotranspiration As Column Colour #cc0000
EndCHART OUTPUT RarityCharts.txt

Chart TempEVTRecent Title Temperatuur en EVT - Recente Data
  PLOT Temperature As SPline Colour #058DC7 zindex 90 LineWidth 10
  PLOT Evapotranspiration As Area Colour #cc0000
EndCHART

Chart CoolingDays Title Overige variabelen
  Plot All AverageTemp
  Plot ALL CoolingDegreeDays
  Plot ALL HeatingDegreeDays
  Plot All Evapotranspiration
EndChart

CHART DailyTemp TITLE Dagelijkse temp met rangecolumn
  PLOT DAILY AverageTemp colour green As ColumnRange
  PLOT DAILY AverageTemp colour black As spline
EndChart OUTPUT ColumnRange.txt

CHART DailyBarometer TITLE Dagelijkse Barometer met rangecolumn
  PLOT DAILY MinBarometer colour Crimson As ColumnRange
  PLOT DAILY AverageBarometer EVAL [ (MinBarometer + MaxBarometer)/2 ] colour black As spline Axis Pressure
EndChart

CHART DailyTempStats TITLE Temp with statistics offset 5
  PLOT ALL AverageTemp colour pink
  PLOT ALL sumAverageTemp EVAL [ Sum(AverageTemp-5) ] COLOUR green AXIS DegreeDays
  STATS ALL AverageTemp SMA COLOUR crimson
EndChart  Output Statistics.txt

CHART DailyRainStats TITLE Rain with statistics
  PLOT ALL RainFall colour CornflowerBlue as column 
  PLOT ALL sumRainFall EVAL [ SUM( RainFall) ] COLOUR crimson AXIS Free
  STATS ALL RainFall SMA colour green
EndChart 

; Documentation:
; https://en.wikipedia.org/wiki/Dew_point
; https://iridl.ldeo.columbia.edu/dochelp/QA/Basic/dewpoint.html
;
; Compare the Dewpoint from Cumulus with the caclculated approximation
; Later I will enter the Cumulus Calculation and have the Humidity be produced by the Davis station
; Nice comparison
;

Chart Dewpoint Title Dewpoint Calculations in CDL
  Plot Humidity
  Plot Dewpoint
  Plot Approximation1 EVAL [ (243.12 * LN(Psat2008) - 440.1) / (19.43 - LN(Psat2008)) ] Axis Temp
  Plot Approximation2 EVAL [ Temperature - ((100 - Humidity)/5) ] Axis Temp
;  STATS Dewpoint SMA colour green
EndChart

Chart VapourPressure Title August-Roche-Magnus Eqn 1980/2008/SubZero in CDL
  Plot Temperature
  Plot Psat2008 Eval [ Psat2008 ] Axis Free
  Plot Psat1980 Eval [ Psat1980 ] Axis Free
  Plot PsatSub0 Eval [ PsatSub0 ] Axis Free
  Plot Avp Eval [ Avp ] Axis Free
EndChart

Chart TempDerivatives Title Temperature Derivatives full in CDL
  Plot Temperature
;  Plot CDLWindChill Eval [ CDLWindChill ] Axis Temp
  Plot AppTemp Eval [ AppTemp ] Axis Temp
  Plot WetBulbTemp Eval [ WetBulbTemp ] Axis Temp
  Plot CDLHumidex Eval [ CDLHumidex ] Axis Temp
EndChart

Chart pwsFWI Title Raw pwsFWI as a chart
  Plot DAILY pwsFWI Eval [ Psat2008ALL * (1 - MinHumidity/100)*HighAvgWindSpeed ] As spline Axis Free Colour Crimson
EndChart Output pwsFWIchart.txt

Chart pwsFWInow Title Raw pwsFWI intraday as a chart
  Plot RECENT pwsFWI Eval [ Psat2008 * (1 - Humidity/100)*WindSpeed ] As spline Axis Free Colour Red
EndChart

@@ Line 148: / Line 148: @@
 ===== Axis Types =====
 The following Axis are possible.
-      Temp, Wind, Distance, Hours, Solar, UV, Rain, Rrate, Pressure, Humidity, DegreeDays, EVT, AQ, ppm, Free
+      Temp, Wind, Distance, Height, Hours, Solar, UV, Rain, Rrate, Pressure, Humidity, DegreeDays, EVT, AQ, ppm, Free
 This only has meaning if there is an [[CDL - EVAL|EVAL]] with a valid expression present. As an [[CDL - EVAL|EVAL]] may modify the value of the plot variable to something completely different, the original Axis belonging to that plot variable may be useless or scale wrongly. Therefore you can choose your own Axis. If there is no valid equation, a warning is given and no axis is generated.