That doesn't seem to work Oli, see screenshot below. The black and red lines overlap. The Rs values behave as travel values either side of the servo centre (the black line) so a value for Rs+ of 0 means no rotation in that direction, a value of 90 for the Rs- means 90 degrees of rotation from centre in the other direction. A typical servo rotates 35 to 45 degrees either side of centre, so values between 35 and 45 will be the normal values. What I can not find is a way to set the angle of the black (servo at centre) line. The spreadsheet is choosing an angle for the black line and it chooses utterly bizarre angles that often lead to the rotation and pushrod going over-centre.

Harry