Calculations from 2 forms that is looked up from main form.

Calculations from 2 forms that is looked up from main form.

Hi,

I'm very new to and need help with calculations from 2 forms that is looked up from main form.
3 forms - Bookings, Price Retail, Price Supplier.

Booking form has fields Booking Number, Price Retail (Lookup field) and Price Supplier (Lookup field). Both lookup fields are bidirectional with Booking form's ID as reference.

Price Retail has fields Price, Discount, Fees, Total and Agent Credits. All currency fields.  Total is populated with script below on user input.

input.Total = input.Price - input.Discount + input.Fees;

Price Supplier has fields  PriceDiscountFeesTotal, Base Commission and  True Commission. Again Total is populated with as above.

Have tried to populate Base Commission with script below. 

pr = Price_Retail[Booking_Details_Booking_Details_ID == Booking_Details_Booking_Details_ID];
input.Base_Commission = pr.Price - input.Price;

But the results are wrong

Please show me the right code and method.
Thank you.
Roger