UP TO: On / Off

Quoted from the Thred manual:

'Toggle between "off" and "on" to see or hide the portion of the design that would come after the selected point.

Use the arrow keys to move forward or back. If you have to edit an area, select the first stitch and turn on the "up to" function.

Then use the right arrow key to watch each stitch, until you reach the stitch you want to change. The left arrow will move you through the stitches backward toward the starting stitch.

Check to see this is turned off if you have suddenly "lost" part of your design. It can be a little startling.'