Hi Riversong
The tool is quite simple and I agree the video clip is not great I had to stop and rewind quite a few times to work it out..
This is what I worked out: follow instructions on ruler to step 3. For step 3 do the first part. Then rotate the ruler 180 degree but place the blunt point of the angle on the mark, not the 'Mark Here" line, cut and all should go well.
Hope this is clear as mud.
Liz in Australia