reservoir 52 through fitting 24 and is exhausted therefrom through pipe 38 that is sealed into screw 70 in the sealed capsule embodiment previously described fittings 24 and 38 are not required screw 70 is adjustable vertically so as to move the bottom stop surface 72 beneath the bottom of chamber 52 is positioned hall effect sensor 60 coil 62 and core 64 by applying a current to leads 82 from connector 80 a current is setup in coil 62 that magnetizes flux focusing core 64 in such a manner as to repulse magnet 54 and drive float 50 up against bottom surface 72 of stop screw 70 as long as energizing current is held in coil 62 float 50 is held against surface 72 at the top of chamber 52 as soon as energizing current is released from coil 62 the float 50 falls through chamber 52 until it rests on the bottom thereof at which time hall effect sensor 60 provides a signal along line 84 to connector 80 as will be more fully explained hereinafter the time between release of energizing current from coil 62 and the activation of hall effect sensor 60 by float 50 is timed to measure the specific gravity or concentration of the fluid within chamber 52 referring now to fig3 the hydrometer control logic will be explained hydrometer logic 90 comprises control circuitry 92 energize and settle single shot 94 clock 96 and counter 98 control inputs to control circuitry 92 appear on lines 91 and 93 to selectively activate measurement of the specific gravity of the reference or working fluids energize and settle single shot 94 is activated by a signal on line 95 to selectively energize ink coil 63.