Data is stored on ActiGraph products in one of two ways: either post-filtered and accumulated or raw.
Post-filtered and accumulated data is typically stored in time buckets referred to as “Epochs.” On ActiGraph devices, “Epochs” are whole-second numbers (e.g., 1s, 5s, 60s, 120s, etc.). For each epoch interval, data samples taken from the accelerometer inside the device at a rate of 30Hz are first filtered then accumulated before being stored in memory. For example, a device set to collect 60 second epoch data will store 30 × 60 = 1800 accumulated samples for each enabled axis on the device every 60 seconds.
GT3X+ devices do not store post-filtered/accumulated data - only raw data.
Devices can be set to store data in raw mode by selecting a sample frequency (12Hz or 30Hz) rather than a whole-second number in the “Epoch” dropdown during the initialization process. When raw mode is set, devices store raw (non-filtered/accumulated) accelerometer data (in units of gravity – G’s) directly into memory at the selected rate (12Hz or 30Hz). When raw mode is enabled, non-accelerometer channels (steps, inclinometer, and lux) are disabled.
Data stored at 12Hz is stored at a resolution of 1/10 (0.1) G (unit of gravity). Data recorded at 30Hz is recorded at a resolution of 1 milli-G (Plus or minus 3G limit).
The GT3X+ product stores data in raw mode at all times. Data collection frequency is variable (30Hz up to 100Hz in 10Hz increments) and can be set during initialization. Similar to other devices, the GT3X+ stores raw accelerometer samples in units of G’s at the indicated frequency. However, unlike other devices it also stores lux (ambient light) samples once per second at all times.
The GT3X+ has a dynamic range of +/- 6 Gs.