With mechancial TV, the number of lines per picture is fixed by the number of holes i nthe disk, so vetical and horizontal rates can't drift separately. Every mechancial system I've ever looked at has had a line sync only. If you get that right, you'll get a recognisable picture, but mayee one in 2 sections (rather like mis-set framining on a cine film projector). But as I said in another post the normal thing was to get the viewer to reard the disk until the picture looked right. It would then stay in sync (you hope). But I don;t think any form of sync was then derrived from the mains, at least not at the receiver. The transmitter disk might well ahve been sdriven my a synchronous motor, but that's not what we're worried about. And in any case I doubt suych a display device was ever used with a microcomputer :-_ However, to sort-of get this on-topic. the OHP displays for the HP48 and 49 calcualtors have a similar issue. The calculatore conenctor has a line sync pulse but not a frame (vertical) sync. WHen you connect the OHP display you might well get an image where the top line of the display is halfway down the screen. You frob a button on the OHP display unit until it's right, it's much the same thing as retarding a mechncial scanning disk... -tony