theres is only one correct way to measure sag and thats to follow the forward curve of the swingarm as it is compressed, to do this measure the distance from the middle of the front sprocket shaft to the middle of the rear wheel nut with the bike on its stand, now move the tape measure from the rear nut to the rear side guard and mark the guard where the distance is the same as the first measurement,this is following the curve of the rear wheel and the correct point to measure the sag from.
With the rear wheel of the ground measure the distance from the rear side guard to the middle of the rear wheel nut.
With the bike now on the ground re measure static sag which should be 25 to 35mm less than the first measurement, get 2 friends and get all your gear on, now get one friend to hold the front fork so you can put your weight on the bike and postion yourself in your normall riding position, get some else to measure the distance again, that should be 95 to 105mm less than the first measurement, if your a moto x rider the rider sag should be closer to 95mm. If you cant get the static sag and rider sag to be between the correct ranges you need to get the correct spring for you weight.