Here is a quote from the instruction manual for the Primus IQ controller.
The Brake Control will HOLD your trailer with
25% of power setting while you are at a standstill
with brake pedal applied for longer than 5 seconds.
b.I , during a braking event, the power automatically
starts out at approximately 13% of the power setting and
increases with deceleration. With the boost on level 2,
b.2 , or with the boost on level 3, b.3 , during
a braking event, the power automatically starts out at
approximately 25% of the power setting and increases
with deceleration.
