I went ahead and moved those floats out of the function and I'll see how it does over the next day. It was doing that about once an hour, but not on any exacting schedule, and it has not miscalculated since I moved those values out. Strange! I guess as long as it works... 
I'll be working this weekend on getting my hardware to play nice together, and hope to have a functioning rig soon. Will update and post pictures!