[Yoda]

I was trying to figure out how Acc. #4 was involved in a stage one stroke. Then I referred to 6-B-4-0 and read this; "Left Arm Power in any form or amount can still be considered #4 Accumulator Action."

So, yes Accumulator #4 is involved in the two barrel stage 1 motion.

The Basic Motion of 12-5-1 is a One Accumulator Stroke (Single Barrel, 10-4-A). And that one Accumulator is an Arm Accumulator, either the Left (10-4-A-4) or the Right (10-4-A-1). If the player chooses to use "Left Arm Power in any form or amount," then the Thrust is Centrifugal (6-C-0-4) and the Stroke is a Swing. If the player chooses to use the Right Arm to drive the Primary Lever (Left Arm and Club), then the Thrust is Muscular (6-C-0-1) and the Stroke is a Hit.

Both Accumulators are referenced in 12-5-1 because both Arms are in Motion -- one Active and the other Passive. And that Motion is identical, no matter which Arm actually drives the Stroke.