if(VatAmount>0, ((VatAmount / Units) / Price) + 1,1) as vatPercentage,
Price * vatPercentage as Final_VAT_amount,
Cost * vatPercentage as Final_VAT_cost,
I just put 1 on the ELSE to have a minimum of 1% for the VAT %
Try this, just check your calcualations Rules..
Hope it helps