I had a 140A the lightweight version in .30-06. I had a devil of a time "trying" to regulate it. It was odd. The barrels shot apart and at a diagonal. Adjusting one or both of the hex screws would simply reverse the diagonal pattern, ie, left barrel at 11 o'clock and right barrel at 4 o'clock would switch to left barrel at 7 o'clock and righ barrel at 2 o'clock. I could get them to regulate on the horizontal plane but a foot apart at 50 yards. I loved that little gun but the frustration of not getting the regulation to cooperate saw me trade the little devil in. I also tried different powders, bullets, loads, seating depths, and a bunch of other tricks, short of swatting it with a large ball peen hammer. I'm now on my 5th double and that little Merkel was the only devil in the bunch. I still presently own a Merkel in 9.3x74 hard soldered barels that regulates with a good composite pattern out to 200 yards. It took some work developing the load but I got it right. My Blaser S2 in .470 regulated well, but I did actually lightly swat the bronze? yoke that holds the muzzles together tho make it regulate on the horizontal plane. The barrel wedge worked very well to draw the left and right patterns together at 100 yards VERY nicely. I found the stock and trigger guard configuration on that gun to be really hard on my finger behind the trigger guard, so that one was replaced with a Merkel in .470 that had a great composite group with the hard soldered barrels. I sold that gun and moved to a Heym in .500NE. Long story, but simply to illustrate that the regulators in the modern double workshops really know their craft. The user adjustable guns in my experience don't seem to behave as nicely as the advertising would lead one to believe. As far as your original question as to "how" the Merkel mechanism actually works, I can't honestly say given I did not take it apart. Please accept my apologies for hijacking the thread a little.

One last thought: the factory target supplied with the Merkel lightweight was also a diagonal pattern. That struck me as odd when I bought the gun that the factory hadnt achieved a good regulation, but the gun was a special order that took over a year to deliver to me so I didn't pay much attention when I picked it up - I thought that it could be "adjusted"' just like the advertising said it could.