I think you want something like this:
var runMin = +runDimension.bottom(1)[0].voltagemagnitude*100;
var runMax = +runDimension.top(1)[0].voltagemagnitude*100;
Then you can set the domain for your y axis:
.y(d3.scale.linear().domain([runMin, runMax]))
Note that bottom
and top
return a data row, so you need to extract the value from it and transform it in the same way that you do for reduceSum
.