Most meters should also have the option to do this for you - have a look in the manual for yours, as you may need to set this up.
I have a Contour Next and it can record the last 800 readings split into fasting, pre and post meal, and non specified categories, and will show averages for each over 7,14, 30 and 90 days, plus more.... All the data can be uploaded to Bayer's free software on my PC which will give further statistics.
Robbity