The MAX MIN AVG is then shown on a chart

I have a table called "test result"

I also have two columns one is 'date' one is thickness 'reading' in mm.

I am trying to calculate the difference in the dates and readings between each pair.

i.e. 5mm loss over 10 days. This is then calculated as a loss over a year after each reading is taken

The MAX MIN AVG is then shown on a chart.
Where do I start....any ideas