I would set the control source to:
=[total]*[taxrate] * Abs([YourYesNoFieldName])

--
Duane Hookom
Microsoft Access MVP


"Sohn" wrote:


Hi, there,

I am building an invoice form which needs tax exemption case.

The first step I took was adding yes/no data type field to customer table.

Then, I put an invisible textbox named taxcode which bring the yes/no field
value when the invoice form loads by using onload command as follow:

If Me.taxcode = 0 then

Me.tax = 0

End If

The tax field has control source. (=[total]*[taxrate];Currency Format)

When a tax exemption customer loaded, the form gives a run time error, "You
can't assign a value to this object".

Could anyone tell me how to fix this problem? Moreover, is there any better
way to distinguish tax/none tax pay customer otherthan what I have used above?

Thank you.