portion like that of the spring illustrated in fig2 rather the spring achieves varying cross sectional mass by a constant force spring that has been modified in its central body portion to exhibit a plurality of areas of reduced width along its length and uniquely exhibits an outwardly tapered end portion as illustrated in fig2 a of the drawings as this spring rolls up from the extended position shown in fig2 it will provide an increase in force at the area designated in fig2 as 69 followed by a decrease in force followed by an increase in force at the area designated in fig2 as 69 a followed again by a decrease in force and finally at the point 69 c at which it is almost completely retracted will exhibit a gradually increasing force referring to fig2 of the drawings still another form of variable force spring having varying cross sectional mass along its length is there illustrated in this instance the varying cross sectional mass is achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of spaced apart apertures u201c ap u201d along its length as shown in fig2 a which is a schematic plot not to scale of force versus cross sectional mass the spring uniquely provides an increasing force in a stair step fashion.