check with your lhs and see what they carry or harbor freight if you have one.i have a mastercool that is for automotive use but works on nitro just fine
I've tried pretty much everyone out there, Outside of dropping $200+ on an Exergen, the O'Donnell the doubles as a stop watch and is backlit is the best one I have found. It was withing 3 degrees of an Exergen less $160.