Hey, Linda --
I have several White machines that are similar. Here is the 765 that is a simple zig-zag, very much like yours:
[ATTACH=CONFIG]501830[/ATTACH]
Here are pictures of the reverse and length mechanism shown from above:
[ATTACH=CONFIG]501833[/ATTACH][ATTACH=CONFIG]501834[/ATTACH][ATTACH=CONFIG]501836[/ATTACH][ATTACH=CONFIG]501837[/ATTACH]