The terms "zero-offset" or "calibration" are often used interchangeably when it comes to your powermeter. Technically speaking, calibration is a one time procedure that occurs at the factory when the powermeter is manufactured. It is the process that sets the relationship between what the crank arm receives as input force to what the strain gauges in the powermeter measure, which is then reported in watts. Each 4iiii powermeter is individually calibrated at the factory to the specific crank it is installed on to ensure an accurate relationship between the powermeter and the crank. Zero-offset is the procedure to remove residual torque that can build up in the crank arm over time. Residual torque can build up due to small physical changes (expanding or contracting) to the crank arm, due to ambient temperature or pressure changes. A zero-offset will zero out the residual torque in the crank so the powermeter is measuring from an absolute zero point (similar to zeroing a precise weigh scale before weighing).
From the point of the rider, zero-offset or calibration are used together to mean the same thing. The 4iiii app uses "Zero-offset", while a cycling computer will often use "Calibrate". As long as the procedure is followed as outlined below, you can be confident that your powermeter is reading as accurately as possible on every ride.
NOTE: you do not need to zero-offset/calibrate your powermeter from both the 4iiii App and your cycling computer before the ride, one or the other will suffice.
When Should I Zero-Offset (Calibrate) My Powermeter?
To get the highest accuracy out of your powermeter, we recommend that you zero-offset (calibrate) your powermeter with the cranks in the vertical position at the beginning of your ride.
If your bike has been stored at a very different temperature than what you are riding in, say from a hot car or garage to the cool outdoors, you should give your bike a few minutes to reach riding temperature before you zero offset (calibrate) your powermeter.
How do I Zero Offset (Calibrate) My Powermeter?
To zero offset your powermeter, unclip from your pedals, dismount, and make sure your powermeter is awake by turning the crank a few times. Ensure that the bike is stationary, and upright (held in a trainer, or leaned against a wall) with the cranks in the 12/6 o'clock position (left crank arm is pointing straight down). Once ready, use the “zero offset/calibrate” option on your head unit or on the 4iiii App to complete the procedure.
Can I perform a zero-offset (calibration) using the 4iiii app?
- Connect your Powermeter with with the 4iiii app.
- Download the free 4iiii app to your phone from the Apple App Store or Google Play Store.
- Open the app and login or create a new account. Once logged in, the app will take you to the Devices tab.
- Spin your 4iiii Powermeter 3-4 times to wake it up.
- Select Add Device.
- Select your Powermeter, and press Connect.
- With the bike upright, position your crank arms at 6 and 12 ‘o clock and hold the bike still.
- Press on the Zero Offset (iOS) or Calibrate Device icon (Android). Select Continue.
- Wait for a prompt indicating calibration was successful.
Find detailed instructions with screenshots in the App Guide.
What do the numbers on my ANT+ display indicate after I zero-offset (calibrate) my Powermeter?
Calibration code for single sided powermeters:
10 – Zero offset successful, ready to ride
20 – Unstable data (bike not stationary)
30 – Low battery (less than 10%)
50 – Calibration error – contact support
99 – Communication error – try reconnecting with the 4iiii App
Calibration code for dual powermeters (first two digits = left powermeter, second two digits = right powermeter):
1010 - Zero offset successful, ready to ride
1020 - Unstable data (bike not stationary) - right
2010 - Unstable data (bike not stationary) - left
1030 - Low battery (less than 10%) - right
3010 - Low battery (less than 10%) - left
1050 - Calibration error - left
5010 - Calibration error - right
1099 - Communication error with right powermeter – try reconnecting with the 4iiii App and paring as dual powermeter
9910 - Communication error with left powermeter – try reconnecting with the 4iiii App and paring as dual powermeter