The 2013-2015 UK Biobank data collection was begun with a set of Axivity AX3 devices in an one type of enclosure and then continued using a newer batch of devices in a different enclosure. This document explains the differences between these two batches of devices.

This resource can be downloaded or viewed using the link: acceldiffs.pdf

If you have wget available (typically on linux systems), then you can also obtain a copy using the command

 wget  -nd  biobank.ctsu.ox.ac.uk/ukb/ukb/docs/acceldiffs.pdf