The Max Force box allows you to enter the maximum force that a probe takes before an error occurs, thus stopping measurement.
A "newton" is a unit of force. One newton is the force needed to accelerate a mass of 1 kilogram to a speed of 1 meter per second per second.
During an analog probing cycle, when the probe first touches the part it continues to move into the part until it reaches this Max Force value. It then reverses direction and moves away from the part. This movement into the part, after touching the part, is sometimes referred to as the contact force. The value is specified in newtons. In a normal deflection mode (DFL) probing cycle, the controller collects data as the probe moves away from the part.