Meter Match Problem

Hi all,
I have been trying to get my meter match problem fixed. I have a 1973 Duster that has the old sender problem that anyone that has bought a repop. I recently bought a Meter Match and I am trying to get it dialed in. I have a old unit that I am trying to get it adjusted with. The problem that I am having is it wont change while I am pushing the up and down buttons. I have it wired to a positive power and grounded directly to the battery. I am using a digital multi tester and the settings wont change. the old unit that I am using is because before that I started on this forum, I didn't know any better. The car has been sitting in the garage for about 7 years and is not licensed and I really want to do it soon. I have been reading and noticed there is alot of good information and members that I have seen and used there advice. Any advice<