Dax - Standard Deviation Based on a Measure

[bravo1563]

Any help would greatly be appreciated.
I have two measures, sum of sales and a sum of forecast units where I'm calculating the variance by month of the [sales] - [forecast units]. I now want to take the standard deviation of my variance measure by month but am unable as it only lets me perform on a column and not a measure. Is there any workaround without creating a calculated column?

Thanks for your help!