Each has its own because once I had the code for the sensor reading and the write to SD the RAM was at ~73% past that I was getting stability warnings thought I had cut code down as much as I could, still new to the coding.
They are all relatively close in the same package.
Taking readings at intervals, did not know there was a way to do a sleep mode. Just having the program wait 60000 ms for example.
Building a multisensor probe that can be put out in a field or such and left alone for prolonged time. Hence the solar power and batteries.