Take a standard leather or biothane M1907 sling apart and reassemble thusly

    On the arm ready to be cinched down

    Grab the frog/loose end and pull it to the right until it's tight enough. Hold that tension and allow the loose end to flop over so you can insert the frog into the holes. It's now locked onto your arm.

    The long strap should be outboard. Give it two twists so it lays licely along the arm and the back of the hand/glove and insert throught the front swivel, rear to front

    Attach the frog end by extending the inboard section straight up toward the swivel

    View from the outboard side

    Notice how flat the sling lays across the arm/hand