efsExternal plot not updating

[pj909]

I want to use an efs (myIndicator) as input to another efs (myStrategy). If I try to plot myIndicator from within myStrategy, the plot does not stay current -- it stops plotting after the script is loaded. I created a very simple example:

// myIndicator
function preMain() {
    setPriceStudy(false);
    setComputeOnClose();        // tried with and with out this
    setDefaultBarFgColor(Color.red, 0);
}

function main() {

    var h = high();
    var l = low();
    var x = h-l;

return (x);
} 

I'm not clear about efsExternal not compatible with setComputeOnClose(). Does this I mean I can't use that in both the calling script and the called script? or only the calling script. I only need to get the indicator value once per bar (not every tick) so I tried various combinatins of using NEWBAR and/or setComputeOnClose. So the question is how to make the code efficient by calling myIndicator once per bar and still keep the plot current?

// myStrategy
var xStudy = null;
var bInit = false;
    
}

function main() {
    if(bInit == false){
        xStudy = efsExternal("myIndicator.efs")
        bInit = true;
    }

    var nState = getBarState();
    if (nState == BARSTATE_NEWBAR) {
        var myPlot = xStudy.getValue(0);
    }
    
    return (myPlot);
}