Use Variable in different DataSet

I need to set a variable with a value from a dataSet "meterDataSet"

Then use that variable as a label in a Table Header where that Table is tied to a different dataSet "multiAssetDataSet"

I have tried putting the following in the onFetch method of various dataSets and also in the initialise method:

reportContext.setPersistentGlobalVariable("Meter1", meterDataSet.getString("Meter1"));

When I try to recall the variable as a label using reportContext.getPersistentGlobalVariable("Meter1"); in the onCreate method of the label in a Table Header where that Table is tied to the dataSet "multiAssetDataSet", I don't see the data in the label.