housing 2 is positioned such that t shaped pivot tab 4 is disposed in abutting relationship with one edge of plasterboard 16 then tape measure 1 is extended outwardly to the desired length and knife 17 is inserted through aperture 8 and then maneuvered to cut the plasterboard along edge 18 following this wall 10 is positioned to overlap edge 18 of plasterboard 16 then knife 17 is inserted through aperture 8 and the entire device is simply caused to slide along opposite edges 18 and 19 of plasterboard 16 so that knife 17 provides a perfectly straight cut along edge 18 if it is desired to measure or mark a circle on plasterboard 16 housing 2 is placed on top of plasterboard 16 whereby rounded pivot tab 4 is placed on the desired point of pivot then pencil 20 is inserted through aperture 8 and ferrule 6 is rotated in a circle around pivot tab 4 which results in the marking of a perfectly round circle shape leaf spring 5 is provided in order to prevent debris from accumulating around t shaped pivot tab 4 a modification of the invention is shown in fig4 and 5 wherein h shaped water level 21 is secured to the upper curved surface of the housing 2 in addition protractor 22.