Text Box Pre Populate

[GMCN]

Any ideas on how I can pre populate a text box on opening a form but
still allow it to have a separate command source?

E.g. I have a sub form with a text box called "Code" which I would
like to pre populate

with [TNG-

I would then like it to be filled with the "Code" which is generated
from series of check boxes to give a code such as

[TNG-CMB

By fiddling around with the Command Source I am able to either have
[TNG- or the code. But I cannot work out how to have both.

Any help will be gratefully received.

 

[GMCN]

Any ideas on how I can pre populate a text box on opening a form but
still allow it to have a separate command source?

E.g. I have a sub form with a text box called "Code" which I would
like to pre populate

with [TNG-

I would then like it to be filled with the "Code" which is generated
from series of check boxes to give a code such as

[TNG-CMB

By fiddling around with the Command Source I am able to either have
[TNG- or the code. But I cannot work out how to have both.

Any help will be gratefully received.

Please forgive my dumbness?? Where I have written Command Source,
please substitute "Control Source"