Pete,
You are absolutely right in your understanding: I have not presented the complete raw data. It is a bit more work to present in the form a graph, for two reasons.
Firstly, although the time is recorded in my notebook, I did not transfer this to my spreadsheet. I have treated all calibrations taken on a single day as taken at the single point on the time axis representing that day. To show how temperature changes during the day i would have to incorporate both the day and the time of day on the time axis. This is not hard to do, but I set out might spreadsheet on a simplified basis since I expected deflation during part of a single day to be of little importance.
Secondly, to display the temperature data as well as the cal const data against day+time, I either need a 3 dimensional graph or I could plot two series of points on the same time axis. I will experiment and see how best to show the raw data.