I am sorry but i am getting really confused over this and i am trying to research online but to no avail.
In my first post i mentioned i have a calculated control of =Nz([GrossOperatingProfit],0)/2.
I have seen that i failed to mention some further information which i apologise for if this is a reason i cannot get it to work.
I have two fields, one called GrossOperatingProfit and the other CommissionDue, The GrossOperatingProfit field is a calculated field and so is the CommissionDue. The CommissionDue field has a control source of =Nz([GrossOperatingProfit],0)/2 so it is halving the value in the GrossOperatingProfit field and displaying the amount in the CommissionDue field. On occasions i will need to edit the CommissionDue field so i am trying to find a way that it will work out the CommissionDue but also let me edit if required. I am realtively new to all of this so i apologise if i do not understand what you mean. Thank you for all your help so far.