This one can be a PITA. There is a very small area near the base of the control rod that you can hook onto and drag either up/down or across to get to the next corner of the ring. On my latest run it's very small, only about four pixels.

hi Chazz...no go , been up and down from top to bottom. when using left mouse button to drag control rod, cursor freezes. Able to engage top , right piston no problem. Cannot move rod otherwise.

You're right, it isn't the base. I had to go back in and check... and it's finicky, but not like what I remembered.

What I found is: When you get the white "interact" dot in the cursor, you have one thing you can do; if you try to do a second thing, the cursor just freezes so long as you hold the mouse button. Even if the thing you just tried to do doesn't work. So:

You'll get an interact dot on the ball at the end of the lever. Click and drag that in (for on/off), left or right, up or down (to change). If it doesn't work, release mouse button and mouse away from it until the interact dot vanishes, click, and try again.

thank you for your patience...still no joy...can sit all day , engaging / disengaging the right , upper piston , but cannot move control rod anywhere else. Followed your instructions precisely, but still nothing. will persist for a bit longer. Have looked on line, checked a walk through, which showed the arrows indicating direction of movement. I don't have these arrows, although they have been there for every other puzzle/interaction. Very frustrating. Again, thank you for your time.

The arrows weren't there for me either; I think they were removed in a recent patch.

I know it was frustrating for me to try and get the handle to move / rotate around this last time, but I did eventually manage it... I can but hope that you'll get it to work also.

thank you ...will persevere...have posted on cyan website....lol

Hey bewley! This is the exact same problem I got stuck on:

https://gtm.steamproxy.vip/app/306760/discussions/0/2250056952642923188/

What you need to do is click (and hold) on the end part of the rod (with the circular ball thing) and drag a LOT in one direction. There's no visual clue that it's working, but once you drag enough the lever will move to one of the other corners. This is the first time I've gotten stuck so far (finally playing again after getting unstuck here...so we're actually at about the same spot in game!)

Well , everyone, have succeeded, followed all advice, Needed to hold rod half way down and hold to move. Clicking and dragging on ball just did the engage/disengage thingy. Feeling very satisfied and smug. lol. Thank you

Good to hear, I'm very glad we were able to help.

SOLVED - I actually worked with Cyan support (who were GREAT btw) and sent my save files and videos of the behavior of the piston couper control not repositioning - it turns out at that you can only reposition the coupler when the target piston is out of the frame of the reticle (viewfinder) of the coupler. Otherwise when you click and drag, the cursor does not move. If there's interest I will post a video. Hope this helps!