Keith adjust how Pleiades mentioned and you only need to do it once to that extent...even easier, drop the lower shock mount and then align the rear swing arm with the front sprocket and adjust. (I couldnt ratchet mine down safely without stressing the strap was going to explode)...then set the slack as described.
Then because everyones preload, weight, height etc are all different....
Now fit everything back up and measure your correctly adjusted chain in whatever method you prefer..ie on centre stand, on side stand, upside down...whatever and mark the position you measured from.

Since you know the chain is now correct, whatever measurement you get will be the correct setting for however YOU choose to measure in the future on YOUR bike, ie without having to ratchet or disconnect anything in the future.

Hope this is clear and enjoy!

Matt.