I know there are apps, but I wanted to tweak my own. Works really well on the Google Sheets phone app.
The Main tab: just put your date/time, reading, and notes in. It will compute various total and daily stats. There are some graphs on the main page showing variance and the total trend. The Daily Grph tab shows your last few days in graph form. You also can easily pull out your high and low since they are highlighted along with lines that are in your goal and/or withing a settable % of your high or low.
https://docs.google.com/spreadsheets/d/1j9zwIcK7SsjJdtPUz35W8AT7FzT4d2hL6XohuKkgPO0/edit?usp=sharing
Let me know if you find it useful or have suggestions. Note in the link, the newest data is old, so the variance and daily charts will show No Data or #DIV/0. Just fill in current data and it will all fill in.
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