Better Pedometer - HELP NEEDED!

Today I have tried wearing both my bangles (2v11) on the same arm to compare the step counters. The results were as follows:
2h sitting at my desk: 0(b77) vs. 866(b87)
Lunch and rest of day sitting at my desk: 621(b77) vs. 5221(b87)

b77 seems reasonable, albeit probably some percentage points on the low side.

Surprised by the massive difference I have recorded some accelerometer data and run it through the test program:

X_STEPS = 6, RAW_THRESHOLD = 17
File, Expected, Simulated, Diff, %, (Original)
halemmerich-walking-2-b77.csv, 150, 77, -73, 51.33 %, (156)
halemmerich-walking-2-b87.csv, 150, 78, -72, 52.00 %, (151)
halemmerich-stationary-1-b77.csv, 0, 0, 0, 0.00 %, (1)
halemmerich-stationary-1-b87.csv, 0, 7, 7, 0.00 %, (10)

I have walked a counted 150 steps for the first files. The plots while walking seem ok, but the stationary b87 has a lot of "movement" for being very still and having both watches on the same arm.

I don't know if it is related, but the internal HRM also seems to be a lot better on b77 than on b87. I have not recorded data for this, but during testing the difference was often > 20bpm. Maybe some hardware issue interfering with both sensors (missing filter cap, bad solder joint somewhere)?

Can I collect some other or additional data?

1 Attachment