Like the example here (http://docs.splunk.com/Documentation/Splunk/6.2.3/Viz/Chartcontrols), I need to assign a parameter to the right-side y-axis. However, I would like the value to be dynamically selected by the user and not pre-configured as in the example. Assigning the dynamic token containing the value to the Overlay does not work (only parameters defined are selectable in the GUI) as the token does not appear to resolve to a value. Is it correct that the only way to accomplish this is to use the input selector (for the right y-axis) post-search? Redrawing the panel using javascript, passing in this token value as the 'overlay' field? I want the user to be able to select which parameter is graphed on the right y-axis on-the-fly.
I've answered my own question I think. The solution basically involves modification of the user interface such that the user is required to input ALL possible options first, then pass this subset (via cascading search, as per 6.x dashboard examples) to another input which is then coded as the 'overlay' value. Here is the functioning panel
<panel>
<input type="time" token="time_token3">
<label>Select a Time Range</label>
<default>
<earliestTime>-30d@d</earliestTime>
<latestTime>now</latestTime>
</default>
</input>
<input type="multiselect" token="lab_param_token2" searchWhenChanged="true">
<label>Select Analyte(s)</label>
<choice value="*">All</choice>
<populatingSearch earliest="-6mon" latest="now" fieldForLabel="lab_param" fieldForValue="lab_param">`wtms_labdata` | fields lab_param | stats count by lab_param</populatingSearch>
<default>Alkalinity</default>
<valuePrefix>lab_param="</valuePrefix>
<valueSuffix>"</valueSuffix>
<delimiter> OR </delimiter>
</input>
<input type="multiselect" token="lab_param_token3" searchWhenChanged="true">
<label>Select Analyte - Right Axis</label>
<populatingSearch fieldForLabel="lab_param" fieldForValue="lab_param">`wtms_labdata` $lab_param_token2$ | fields lab_param | stats count by lab_param</populatingSearch>
</input>
<chart>
<title>Multiple Analytes by $lab_location_token$</title>
<searchString>`wtms_labdata` treatment_plant="$treatment_plant_token$" $lab_location_token$ $lab_param_token2$ | timechart span=1h values(result) by lab_param</searchString>
<earliestTime>$time_token3.earliest$</earliestTime>
<latestTime>$time_token3.latest$</latestTime>
<option name="wrap">true</option>
<option name="rowNumbers">false</option>
<option name="dataOverlayMode">none</option>
<option name="count">10</option>
<option name="charting.axisLabelsX.majorLabelStyle.overflowMode">ellipsisNone</option>
<option name="charting.axisLabelsX.majorLabelStyle.rotation">0</option>
<option name="charting.axisTitleX.visibility">visible</option>
<option name="charting.axisTitleY.visibility">visible</option>
<option name="charting.axisTitleY2.visibility">visible</option>
<option name="charting.axisX.scale">linear</option>
<option name="charting.axisY.scale">linear</option>
<option name="charting.axisY2.enabled">true</option>
<option name="charting.axisY2.scale">inherit</option>
<option name="charting.chart">line</option>
<option name="charting.chart.nullValueMode">connect</option>
<option name="charting.chart.sliceCollapsingThreshold">0.01</option>
<option name="charting.chart.stackMode">default</option>
<option name="charting.chart.style">shiny</option>
<option name="charting.drilldown">none</option>
<option name="charting.layout.splitSeries">0</option>
<option name="charting.legend.labelStyle.overflowMode">ellipsisMiddle</option>
<option name="charting.legend.placement">right</option>
<option name="charting.chart.overlayFields">$lab_param_token3$</option>
</chart>
</panel>