Reverse engineering a statistics data file from my insulin pump controller

What I would do next is try and find some numbers. There's a bunch of ways the numbers could be encoded:

• Ints (1, 2, 4 bytes, various endianness)
• Floating-point (of various sizes)
• Fixed point or some other strange format

You have the advantage of knowing some numbers that are going to be in there, since you can see the data on the screen. So I'd look for those numbers in the file (in the various formats above). This should give you some data, at minimum.

Next, you mention timestamps. Timestamps are usually pretty easy, because they're invariably 32-bit unsigned ints, and you have a good ballpark range (time() +/- a few 100,000). So look for ints near there.

You can do all this by hand with a hex editor or write a little script. Once you start getting some data out, look for patterns. This should help a lot with finding more interesting fields. Good luck!