4iiii Update, May 1, 2015

Some new PRECISION riders are using bike power for the first time and have sent us great questions that we’ll do our best to answer in these blogs. This week, we will address the ever-confused issue of calibration/zeroing/re-zeroing. The whole concept is really much easier for you, the user, than it first seems. Here’s the simple summary:

PRECISION power meters use proprietary strain sensors that provide you with accurate power measurements. Initially, PRECISION needs to be “taught” how to translate a certain force to a specific power value. We do this initial set up for you in our factory with certified weights and we refer to it as Factory Calibration. This calibration procedure generates a linear function (also known as a calibration curve) which is unique to your PRECISION and crank combination. The calibration values on the 4iiii calibration card you receive with your pod denote the two values associated with the curve obtained at the factory. They will not change over the course of PRECISION’s life.

Once outside of our factory, your PRECISION sensor – just as all power meters – will have its own signature response to environmental and temperature changes. This is normal and very similar to how you need to reset your weigh scale to ‘zero’ before each use. The changes can shift slightly upwards or downwards which “offsets” the calibration curve established in factory and causes you to obtain higher or lower values than you actually want. So, in order to get the best and most accurate power reading, your power meter needs to be zeroed before a ride and after any large temperature fluctuations. Note: Most (if not all) head units refer to this step as ‘calibrate’ although some will name the action ‘zero’ or ‘re-zero.’ All head units that support power will have this easy-to-use utility that is activated with only a push of a button

When you successfully zero PRECISION, you should see two numbers alternating on the screen of your head unit or bike computer. Normal ranges for these numbers are between 8000 to 11000 and 18000 and 21000.

If you get numbers of 999 or -999, that means the unit isn’t settled or the crank arms are in the wrong position. To correct this, eliminate any wind or movement factors and try again.

For more information on this and specific zeroing step, please read the PRECISION User Manual at 4iiii.com/PRECISION