Extensor action...keeps the inert left arm in check...
Actually, the opposite is true: The effortless Checkrein Action of the Left Arm (which serves by just 'being there') restrains the continuous Extensor Action of the Right (6-B-1-0). In other words, by serving as its leash, the Left Arm keeps the otherwise unruly Right Arm 'in check.'
The Action derives its name from the short checkrein on a bridle that prevents a horse from lowering his head.
Threaded Mode
