The link to the Anaplan Community provided returns a 404 error for me but Anaplan does have a Descriptive Statistics model that provides insight into how you can perform calculations such as finding the standard deviation. I'm attaching a screenshot for anyone else that stumbles onto this question but doesn't want to download the model
In this method though I break one of the PLAN tenants. I have a back and forth calculation between the transaction module and the calculation module because the dimensions are the same. But it's pretty straight forward.