I simply could not make my Campagnolo Record 10s derailleur shift correctly on my TT bike. It would skip over the 4th gear and not pull the right amount at each gear in general. It turned out to be more than one thing that was wrong:
Campagnolo provides a PDF 035_231_User_manual_brake_lever_bar_end_mechanical_Campagnolo_REV_05-01.pdf that actually contains all the information needed. Just mount things in the same direction and order as in the exploded view and you will be golden.
Although it is clearly (well..) stated in the exploded view, it is easy for the human brain not to notice the notches there that indicate the correct orientation. And if you do not, there is just a 50/50 change to get it right:
10 speed means there must be 9 clicks between position 1 and 10. The 10 speed index ring (SL-RE319) has 27 notches, 9 for each of the 3 springs. (It also has the text “10s” stamped in it.) Hence the 9 speed index ring (SL-RE219) has 24 notches, 8 for each of the 3 spring.
Why was there a 9 speed index ring in my shifter? I have no idea, but replacing it with a 10 speed SL-RE319 index ring obviously did the trick for me.
Make sure to mount the index ring as per the manual, and assemble with the lever in the position for the lowest gear/smallest ring.