Abstract: An easily calibrated indicating device for monitoring pressures or other parameters that vary, comprising a housing having a scale plate with indicia representing a range of values, and an indicating member movable over the scale plate, for designating various values thereon. A driving permanent magnet is movable in the housing, and responds to changes in the parameter being measured. A movable follower permanent magnet is also provided in the housing, for reacting with the driving magnet, the follower magnet in turn being connected to the indicating member so as to shift the same in response to movement of the driving magnet. A third, trim or calibration permanent magnet is provided, which alters the reaction between the first two magnets, thereby enabling either an expansion or else a contraction of the range of movement of the indicator member to be had as it responds to a predetermined change in the condition being measured.