Here's  how to calibrate the EXP pedal on the GT-100.

1. Press the SYSTEM button.

2. Turn knob 4 to select the PDL CALIBRATION icon.

3. Following the prompts in the right-side display, move the EXP pedal to the min (heel-back) position.

4. Press WRITE.

5. Press the EXP pedal all the way toe-forward until it stops.

6. Press WRITE.

7. Turn knob 8 to choose the desired Threshold value (1-16) for the Toe-End switch under the EXP pedal. A lower value allows the switch  to be activated with the least amount of pressure. With higher values, more force is needed to activate the switch. 

8. When you're finished, press WRITE. The new settings are stored.