How to convert data in text boxes.. e.g. Liters to gallons

[Gustavson]

Here's what I have. A combo box in which you can choose from Liters or gallons. If Liters is selected, I want to display in a seperate text box, what that is in gallons. How do I set up the text box to first recognize Liters and then do the conversion and display result.. Also, if gallons was selected, I don't want any calculation done, but just mirror the data in the text box.... Hope this is enough info..
Thanx
Gustavson

 

[Gustavson]

I forgot to mention there is a third box in which you enter the quantity of product..
So, Here is a e.g.
user inputs quantity in text box and selects unit in combo box:
100
Liters
displayed in text boxes is quantity and unit(gallons):
21
gallons

 

[RegionsRob]

Put the following in the Control Source of the Result box:
=iif(txtCombo = "Liters", CStr(txtQuantity * .2642) & " Gallons", CStr(txtQuantity * 3.7853) & " Liters&quot

where txtCombo refers to the Combo box and txtQuantity refers to the quantity box.