Thanks for your help on this one.   Yep, since it's moving the full sweep and zeroing when it's supposed to I think I'll be OK.  Funny story: I asked my 5 year old son to watch the gauge for me while I held the sending unit to ground.  He did start yelling at me when it moved and when asked he told me it was reading zero, but since he doesn't always listen to instructions real well, I decided I'd better ask mama to watch the gauge.  He was right - should have trusted him!