damper 118 presents a resilient tip for resisting impact due to the limited swinging movement of the arm 80 during tensioning and release of the cable 70 second strength monitoring station 18 is adjustably mounted on bars 118 and 120 connected to frame 12 at their bottom ends and by header 122 secured by bolts extending through the cover 14 to a bar connected to beams extending rearwardly from crossbeam 34 connected to upright supports 28 and 30 the station 18 includes a receiver 123 and a block 124 interconnected by bolt 125 which passes through receiver 123 the receiver may be tightened by the bolt 125 to bring the receiver 123 and the block 124 into engagement with bars 118 and 120 as shown in fig5 by turning threaded knob 126 the block 124 includes a nose 127 which receives therethrough a bolt 128 mounting second load cell lc2 thereon the block also presents two parallel guide rods 132 and 134 the guide rods 132 and 134 are secured at their front end to block 124 but are freely shiftably received within respective channels 129 and 130 of engagement member 136 which is covered with padding 138 the load cell lc2 is provided with rearwardly extending threaded rod 140 which is threadably coupled to engagement member 136 whereby force applied to the engagement member in a direction parallel to guide rods 132 and 134 is carried by second load cell lc2 which is fixed to nose 127 third strength monitoring station 20 is swingably carried on column 24 for movement about a vertical axis as illustrated in fig1.