Formula to count to a certain number

I'm helping a local business create a tracker that will track energy consumption. Basically just meter readings. I've got the tracker down for the most part however the meter readings start over at 100,000 then starts back over at zero. Which leaves me with a huge negative balance. Is there a formula that will calculate two cells up to 100000, then count the difference from example 95,000 to 5,000 (answer would be 10,000). There's 150 meters, otherwise I'd manually change the values.