There are number of methods you can use.
For example, if you have two fields called txtTest1 and txtTest2 and you want to update txtTest2 every time txtTest1 is modified you can use code to chage the value as shown below…
Private Sub txtTest1_AfterUpdate()
Me!txtTest2 = Me!txtTest1 ‘Update txtTest2 field on this form with value from txtTest1 field
With this method you will be abe to modify the value in txtTest2 independetly as well.
Another method you could use is to link txtTest2 Control Source to txtTest1 as shown below…
1) Click on Properties
2) Click Data tab
3) Enter =[txtTest1] in the Control Source field so it looks like this
Control Source ………..=[txtTest1]
This will link two values, however, you will not be able to modify the value in txtTest2 independetly with this method. It will be locked for editing.