Hired-Hand System 500 Power Curtain Controller - Manual (Page 11)

System 500™ Power Curtain™ Controller 9
6.2.2.7.3. Variable Offset Adjust
The variable offset is the number of degrees from target
temperature at which the variable speed fan will be at
minimum speed. For example, if target temperature is 75
degrees, and the variable offset is set at minus 5 degrees, then
the fan will be running at minimum speed when temperature
equals 70 degrees.
Example:
Minimum 40 percent
Offset -5 degrees
Span 10 degrees
Target Temp 75 degrees
The variable speed fan will run at 40% when the inside temp
is 70 degrees (target - offset). The controller will increase fan
speed if inside temperature is rising up until 80 degrees
[(target - offset) + span] at which point the fan would be
running at 100 percent.