With the spring preload you adjust the SAG number, witch, as a rule of thumb, should be 2/3 of your suspension travel when you sit on the bike. In the case of the 701 the number is about 90 mm (for 135 mm of back suspension travel).
So, you measure from the back wheel axle to the “VITPILEN” writing on the tail, with no load on the bike (A), and then you get on the bike, in full gear, and have a friend take the same measurement (B), and do the math.
A – B sould be around 90 mm. If it’s larger than 90 you should decrease the prealod, and the opposite if A-B is lower than 90. Re do the B measurement every time you change the preaload, and once in a while…