Another Early Strain Gauge

The bay pointed me to another early use of a strain gauge phono cartridge from 1950.  Like the Capehart from 4 years earlier, this one also plays both sides of a record but in a very clever way.  In looking at the pictures I had some ideas but couldn't figure it out. (pictures from the ebay auction by Vintageaudiophilia)

I finally gave up and went to google and found this youtube video and this is so simple and clever

It is a 13 minute video so to cut to the chase go to 3:35 for one side and 6:55 for the switchover.  I knew those threewheels had something to do with it but couldnt figure out how they would reverse the rotation.  IT took me about 15 seconds of staring at it to get my dyslexic brain to tell hand to slap forehead.

I don't plan on spending $1K on these so have at em.

dave