u2032 r u2032 22 varies preferably linearly from a minimum r u2032 min to a maximum r u2032 max mr 11 and mr 12 are designed such that their resistances r 11 and r 12 are a fraction p u2032 of r u2032 max when exposed to the maximum magnetic flux density and mr 31 and mr 32 are designed such that their resistances r 31 and r 32 are a fraction q u2032 of r u2032 min when exposed to the minimum magnetic flux density where p u2032 and q u2032 have preferably values between greater than zero and one hence r 11 p u2032 r 12 p u2032 r u2032 max and r 31 q u2032 r 32 q u2032 r u2032 min values for p u2032 and q u2032 greater than one are permissible but there does not appear to be any benefit in doing so r u2032 21 a u2032 a 2 l u2032 r 12 p u2032 1 u2212 a u2032 a 21 u2032 r 32 q u2032 5 r u2032 21 a u2032 a 2 l u2032 r 11 p u2032 1 u2212 a u2032 a 21 u2032 r 31 q u2032 6 r u2032 22 1 u2212 a u2032 a 22 u2032 r 12 p u2032 a u2032 a.