Almost any
stainless steel dial caliper works reliably even some of the cheapo Chineese ones for $20 better yet get a Starrett model120 6'' Look on Ebay you may get a used one for around $40 .
I'm not a big fan of those electronic ones.
Here are a couple:
This is the better version of Starrett- Rack gear is open and some are in the padded case. Always look to see if the pointer is at 12:00. If not it's more than likely dropped or a chip got into the rack.
http://cgi.ebay.com/Starrett-Dial-Ca...item3f0c69f12c
I think these ones are Starretts cheap version. Look at the rack gear-It's covered and it comes in a plastic case.
http://cgi.ebay.com/Starrett-120A-6-...item43a8a3151a