I've never used the field validation before so its new to me but this should be an easy one for some of you.

I'm working with 3 fields

KitsInOut - text field with 2 option (Sent or Received)

CountIn - Number field holds number of kits in

CountOut - Number field to hold number of kits sent out.

I want to make sure that if KitsInOut is set to Sent that no one can put a value in the CountIn field and if KitsInOut is set to Received no one can put a value in the CountIn.

Any advice is greatly appreciated.

Wouldn't it be easier for the user to enter data into two fields only (either CountIn and CountOut or Amount and Type)?

it might be but we have to send a payment for the CountIn (for for like every 50 in) so i was trying to separate the the number in and out a little to make reports and figuring out what we need to pay a little easier.

but maybe i'm doing it wrong.

You can still separate the ins from the outs - but that's not the user's job, IMHO. It's always difficult to advise regarding workflow, esp. when given so little, but I think I would make the user enter the amount (say into a global field) and click one of two buttons. Then have a script sort it out behind the scenes.