18 and the lower arm 16 form an acute angle see fig1 to a position wherein the upper arm 18 and the lower arm 16 form an obtuse angle see fig7 conversely retraction of the second assembly 86 causes the upper arm 18 to pivot relative to the lower arm from the position wherein the upper arm 18 and the lower arm 16 from an obtuse angle to the position wherein the upper arm 18 and the lower arm 16 form an acute angle it will be appreciated that the second assembly 86 may selectively assume any position from a fully retracted position to a fully extended position the primary boom 22 is entirely conventional and may be an articulated u201c knuckle u201d boom or a multiple section extensible boom the boom 22 carries at its upper end a conventional bucket leveling device 100 which is secured to the personnel bucket 24 and serves to maintain the bucket level during all movement of the boom the device 100 includes an upper mounting surface 102 with an downwardly extending socket not shown this socket is designed to receive the component 28 of jib unit 10 with the locking pin 30 extending thought the socket defining body of the device 100 and through one of the locking holes 31 to detachably mount the jib unit 10 to boom 22 note that the unit may be mounted in two positions relative to bucket 24 by selection of an appropriate mounting hole 31 furthermore the locking pin 30 is hand removable thus enabling a user to quickly and easily rotate the unit 10 relative to.