True Fitness Touchscreen Elliptical Owner's Manual page 20

Heart Rate Zone Display:
These are calculated based on an estimated maximum heart rate of 220 minus
your age. Therefore they are only available if you enter your age correctly. Note
that this estimated maximum heart rate is only an estimate. You must use either
a transmitter strap or the contact heart rate system for this display to work. A
wireless heart rate strap is preferred.
The ESX Touchscreen
Chapter One: Basic Operation
ESX Touchscreen Owner's Guide
20