how do i use the s key on tec cash register without losing all totals?

The following procedure should work on TEC registers of recent vintage:
1) Unplug the register from power.
2) Insert the S key and turn to the unlabelled position one click clockwise past the Z position (referred to as the 'BLIND' position in the manual).
3) Plug in the register.

If this doesn't work, post again with the model number of your register and I'll see if I can help.

Steve
December 2009