springs falling outside of a predetermined tolerance for example adjusting half of the springs would cut variation in half adjusting that half of the springs having the worst variations would cut variation by more than half fig5 a and 5 b are cross sectional views of an embodiment of the infusion pump incorporating a stacked series of shims 81 of equal or varying thickness to adjust the force exerted by the spring 60 on the plunger 40 for example the shims 81 could be shaped as disks or washers fig6 a and 6 b are cross sectional views of an embodiment of the infusion pump using a helical shim 82 that can be trimmed to a desired height to adjust the spring force the manufacturer would simply cut off the proper number of coils to achieve the desired height for the helical shim 82 fig7 a and 7 b are cross sectional views of an embodiment of the infusion pump incorporating coaxial beveled segments 83 to adjust the spring force this embodiment is similar to the device used to damp a swinging door two beveled cylindrical segments are stacked atop one another rotating the cylindrical segments with respect to one another increases or decreases the.