shown by arrow a and raises magnet 802 away from shuttle 806 the increased separation between magnet 802 and shuttle 806 decreases the magnetic attraction between the two until the force of compressed drive spring 804 exceeds the force of magnetic attraction at this point drive spring 804 is allowed to extend firing sensor 818 into the user 39 s skin the degree of magnetic attraction between shuttle 806 and magnet s 802 may be varied by the size number location and or polarity of magnet s 802 for example a user may place additional magnets 802 on top of pivot arm 812 to further compress drive spring 804 this in turn may provide a higher sensor insertion velocity in alternative embodiments magnet s may be used in conjunction with previously described embodiments to affect spring compression in such embodiments no magnet may be used for a low speed setting and one or more magnets may be used for higher speed setting s in other embodiments not shown separate cartridges may alternately be installed by a user each cartridge having a different spring rate for providing different insertion characteristics alternatively a wind up type constant force spring may be utilized to vary the spring force such an arrangement may also use a ratchet and lock type mechanism to affect the winding in yet other embodiments internal dampeners or other features may be used to allow adjustment of the firing characteristics of the inserter for example air bladders movable walls or contact areas can be employed to increase decrease or remove friction thereby allowing sensor shuttle speed.