Electronic devices to measure SG / temperature do exist for salt water aquariums... take a look at this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7709700558&category=3212
"Specific Gravity range (1.000 - 1.030 S.G.), accuracy +-0.002 S.G."
"Tempurature range (0 - 70C) (32F - 158F)"...