I wouldnt trust those analog gauges at all. I highly recommend getting an Acurite digital gauge which also has a humidity gauge. http://mobile.walmart.com/ip/Acu-Rit...mometer/896347
Also, if your UTH isnt already controlled by a thermostat, that's a must. If you want to go a cheaper side of thermostats, you can always get a Hydrofarm thermostat or go with something better like a Herpstat. Without anything controlling your UTH, your snake can get easily burned.
Like I said before, if the temps gets as low as 73 in any part of the tank, that's way too low. It should be a minimum of 77. Here's a good thread in how to set up a glass terrarium: http://ball-pythons.net/forums/showthread.php?t=201740
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