[Water Warrior 2]

Can you get the rear wheel off the ground? Will assume you can. What I would do is the following.
Find the mid point between the sprockets and measure the bottom of the lower length of chain from the floor. Rotate the tire a bit and repeat. Repeat again and again till you have found the tightest(least slack) position of the chain. Measure that..........now lift the bottom length of the chain and measure the difference. I would set the slack at 1 inch and call it a day. Hope this helps. Lynda's GZ ran nicely with this measurement.