Help! I'm stumped - how do I balance my hydronic radiant floor heat.

I have an older house (originally built in 1925) that had an addition that was done in mid 80's. Part of the house has hydronic floor heating. There is a 4 port manifold on the floor heating. There what I am sure are flow valves in the manifold on one side. I can't for the life of my figure out how these adjust. The valve is brass and has an outer ring with numbers on it, then a small ring inside that with a little key hole in it, and in the center a pin. Then there is a plastic cap that is a key to turn the dial in/out and then when you screw the cap on it pushes the pin.

How do you adjust these? I've done days of searching and can't find a picture of these values (I've got one, but doesn't appear easy to post). Is in or out more flow? Does the pin need to be in or out? What is the relevance of the numbers on the dial?

Thanks, Chris

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