PO Price Variance Tolerance against Valuation Price

Hi Experts,

I am tiring to turn on the configuration "Purchase Order -> Set Tolerance Limits for Price Variance" (for PE-Price variance: purchasing) as an error message.

I am wondering about how its act for Unit of Measure differences (Base Unit in EA and Order Unit in PACK) and Currency differences (USD to EUR).

Please provide your experience.

Thanks

John K.