Here's step by step:

Step 1: Assign Channel 6 to SW C.

Step 2. Change Endpoint of CH 6 to 20% when SW C is in the UP position

Step 3. Change Endpoint of CH 6 to 20% when SW C is in the DOWN position

Step 4. Place SW C in the CTR position.

Step 5. Adjust linkage so that the correct Takeoff setting is achieved. i.e. 20º

Step 6. Place SW C in the UP position

Step 7. Adjust endpoint so that the Flap is in the Full Up position (0º).

Step 8. Place SW C in the DOWN position.

Step 9. Adjust endpoint so that the correct Full Down setting is achieved. i.e. 50º

Step 10. Go Fly!

In effect, one uses the takeoff flap position as the centre point (in reality an ofset centre point) and adjusts the other ends to suit.

Dennis