My wife reckons that nobody is interested in this, but I'll share it nonetheless.
The spreadsheet where I record all my sugar is here. I've shared it to my web site folder, so hopefully you can see it. It comes down as a .xlsm file, which can be recognised by Excel 2016, which you get from Office 365. XLSM presumably means "a spreadsheet containing macros".
The spreadsheet has about 4 rows of dummy data, just so you can see what you have to enter. You just need to enter the time, date and value. Other columns are optional i I record how much insulin I take, and what monitor I use to measure - and those with a grey background are calculated.
To calculate statistics, just hit the button in the top-right, and follow the instructions. I've put a little macro under there which will ask for the first row you want to calculate stats for, and the last row. It'll then work out when was "one month ago", and write the number of entries, the average and the standard deviation in columns E, F and G. Please note that where you just have one reading for the last month, the mean will just be that reading. And, you need at least 2 readings during the last month in order to calculate a standard deviation, so with just this sample data, each cell in Column G shows an error (which will go away as you add that second row).
The macro is very basic, its main purpose is to work out which days are within the last month. it is quite crude, will expect the data to be in chronological order, and will behave unreliably id not. I really developed it for myself rather than for public consumption.
Software provided on a "best endeavours" basis. The macro is written in a language called VBScript, which I've never ever seen in the last 10 years! You can view and change the source code, in any case.
BEFORE YOU START: Please note that although I currently volunteer for both the Stroke Association and Age UK, the views expressed in this blog are strictly my own. I am not a spokesperson for either (or, indeed, for any) organisation, and I accept complete responsibility for the views expressed herein. As indicated by the domain name, I am based in the UK and the blog therefore has a UK bias - I've tried to use the Glossary to explain any ambiguous terms, but if you think there is anything I've missed, please message me.