Thanks both. I read the lesson, and am getting a better understanding of the chrono mechanism.    Practically speaking, how should I adjust the finger? Bend it a bit with two pairs of tweezers? Is this possible with it in situ, or does it need to be taken off and on repeatedly until it's right?

Unitas.   https://ranfft.org/caliber/10349-Unitas-6498   Why isn't it working? Another link with the incabloc  https://calibercorner.com/eta-caliber-6498-1/  

I have been asked to repair a pocket watch.  I have done the disassemble and checked all parts. Not going to rush.  It has a dial - Arnex. Can anyone help me with the movement please. TU 6498 are the markings Thank you Ross  

Thanks for the input - but I don't think this is the case either. I have inspected the spring and it looked fine with the bridle locked against the ridge on the barrel wall.  And as I said, I did manage to put a full wind on it using my tweezers without any slipping. @JohnR725 You might be right about pushing down when I use the tweezers! And yes I am aware that this is a cheap movement! I have just taken the watch back out of the case and removed the dial to see if I can see better. Strangely I was able to wind it  a few times without slipping when it was out of the case .  But when I try to release the power on the mainspring by holding back the click and slowly letting the crown turn, it slips. 

I was afraid of something like this and yes the pictures helpful for those that have never seen one of these. The problem with a watch like this made at a bargain price and they do things a little bit differently.   Nitpicky clarification required? When winding with the crown versus pushing with the tweezers visually is it exactly the same? Then when you whining with your tweezers are you pushing down at all? It's possible the mainspring is slipping on the other side farther into the watch. As I said these are made differently cheaper than a standard watch and we probably need a better image of the mainspring barrel itself. Like for instance you notice the upper pivot well if you do you're seeing things as there is no upper pivot. So another words is a strap holding the barrel in place and it's definitely made differently than the standard watch. Which means conceivably it slipping on the other side as things have worn out and you may not be a loose see that on the other side. One of the annoying problems with technical information that you download is conveniently when it was scanned the technical was not because they just wanted the parts lists. So we can see that the mainspring barrel in this case doesn't have an arbor. In other words it goes together a little bit differently than a standard watch and it's possible that it still has defect and is slipping somewhere in here. Then he is a website that shows a few pictures but not how the barrel goes together or the barrel itself which is unfortunate. https://17jewels.info/movements/e/eb/eb-8800/   EB_EB 8800etc.pdf