What resolution will my heart-rate data have?
In general, during non-activity periods, your heart rate is recorded at 5 second intervals.
During activity periods, your heart rate is nominally recorded at 3 second intervals. Sometimes this frequency increases to 1 value per second, but this may correlate to periods when your device is having difficulty obtaining a reliable reading (eg, due to being worn incorrectly).
The exact time of individual heart beats is not recorded, so heart-rate variation analysis requiring that level of precision is not possible.
(These conclusions are based on experience with Fitbit Surge and Charge 2 devices. Other devices may behave differently.)
Why doesn't my .CSV file contain my heart-rate readings?
This could be caused by incorrect settings when opening the .CSV file in your spreadsheet (or equivalent). In particular, ensure that fields are comma-delimited.
To verify that your .CSV file does actually contain your data, try opening it in a text editor (eg, by appending .TXT to its filename). If the data is present, try using different settings when importing it into your spreadsheet. If the data is missing, please contact me.
Here's a small example of a correctly-populated .CSV file that you can compare with your own, and experiment with.
Can I get my sleep data?
Not yet. It's on my to-do list. Feel free to let me know that you want it, and I'll shuffle my priorities.
Can I get more than one day's data at a time?
Not automatically. Allowing multi-day queries would make it easy for people to download large amounts of data very quickly. This web site costs me money to operate, and I need to limit that cost. Moreover, Fitbit staff are also keen to ensure that this site does not put an excessive load on their servers (which are the source of all data made available here).
You are the only one who sees your data. Full details are here.