in that case would need to apply only 3 pounds of pressure to lever 158 different ratios may be introduced to optimize distraction force while minimizing injection pressures the pressure application process is guided by normal surgical principles by visual checkpoints and by a safety gauge that illustrates the amount of expansion that has been exerted in direct correlation with the implant expansion process the gauge indicates the height of the slave pistons and thus the vertical and angular expansion of the sec this translates to an ability to clarify the percentage of lateral expansion that is if the surgeon chooses to create an angle he expands the right slave cylinder for example 14 mm and left slave cylinder 12 mm the master cylinder 154 preferably comprises transparent plastic to enable visual indication of the height of the hydraulic fluid therein or a translucent plastic syringe to facilitate exact measured infusion of the slave cylinder implant expanding pistons a knob 159 for setting gauge height is provided in each cylinder an indicator attached to the knob registers the cylinder height with respect to a fill line bleed line or maximum height line the master cylinder and slave cylinders are filled with hydraulic fluid air is removed by bleeding the cylinders in a well known manner the knob indicator is registered to the bleed line a series of incremental marks are provided between the bleed line and the maximum height line to show the surgeon the exact height of the slave cylinder in response to the surgeon 39 s control inputs to the master cylinder it will be appreciated that the master and slave hydraulic system interaction can have many equivalent variations for example the master cylinder function of master cylinder 154 also can be provided by one or more syringes.