Simple Formula Field Not Working

Simple Formula Field Not Working

I have a formula field with it's value set to a decimal field - it doesn't display anything.

Here's the details;
I have a decimal field which is updated from a drop down field's on input event.

I have a formula field which (at this point) should just display the value from decimal field.  So it's formula is simply the decimal field name.

It doesn't update.

In the end I want to display the difference between two decimal fields (i.e. field1-field2) in the formula field.

Am I caught in another "Catch-22"?
Thanks,
Dennis