True Fitness Treadmill ES9.0 + ES7.0 Owner's Manual page 22

Zero-grade walking or running intervals are in one-minute
segments. Grade changes are permanent; speed changes affect the
current one-minute segment only.
Zero-grade gradually increases speed then decreases speed,
changing once per minute. Grade changes are permanent; speed
changes affect the current one-minute segment only.
Special Workouts
Chapter One: Basic Operation
Changes in Speed
Changes in Speed
ES Treadmills Owner's Guide
Walking
and
Running:
Speed
Intervals
Walking
and
Running:
Speed Ramp
22