the exception of negligible errors i e roughly the value of iron reluctance r fe can be said to depend solely on the value of flux u03c6 t whereas the value of gap reluctance r o depends solely on position x t i e r x t u03c6 t r fe u03c6 t r o x t n i t r fe u03c6 t u03c6 t r o x t u03c6 t by resolving the last equation shown above with respect to r o x t the value of gap reluctance r o can be calculated given the value of current i t which is easily measured using an ammeter 20 given the value of n which is fixed and depends on the construction characteristics of coil 17 given the value of flux u03c6 t and given the relationship between iron reluctance r fe and flux u03c6 known from the construction characteristics of magnetic circuit 18 and the magnetic characteristics of the material used or easily determined by tests the relationship between gap reluctance r o and position x can be determined relatively simply by analyzing the characteristics of magnetic circuit 18 an example model of the behaviour of gap 19 is shown in the equation below given the relationship between gap reluctance r o and position x position x can be determined from gap reluctance r o.