You should either have a digital thermometer probe on the bottom of the glass to check how hot the UTH heats up the glass or your can use an infrared temperature gun. The glass shouldn't be hotter than 90 F.
In regards to your temperature gauge, if you have the circle analog gauges they're not very accurate so you should consider replacing them with a digital thermostat which should run you about $10-20 bucks at stores like Walmart. Most people here prefer something like this so that way you can put the probe on the glass where the UTH is and then also monitor ambient temp and humidity:
http://www.walmart.com/ip/Taylor-152...meter/24727251
http://www.walmart.com/ip/896347?www...tRedirect=true