with all the good info on springs going around how can i tell if my springs are actually bad?

if i measure(on level ground) from the drivers side tire to the top of the arch say its 2.25 inches then go measure to passenger side it will be somthing like 1.5 inches so im assuming after 11 yrs the sprngs have started to really sag at different rates?

other than the hight difference is there a slightly more scientific way to see if springs are bad?