are provided to the 5 u00d7 7 dot matrix display chip 38 the chip is a model hdsp 4501 manufactured by hewlett packard the lines from latch 86 each pass through a resistor 92 having a value of 470 ohms to the row input of display chip 38 the purpose of this resistor is current regulation which controls led intensity the output from latch 88 goes to the column input of chip 38 the dot matrix chip display 38 defines a 5 u00d7 7 matrix of leds this display will give a visual display of the slope of the surface being measured as can be seen the device of the present invention will define a reference plane electronically and display the slope of that reference plane to the user this slope corresponds to the slope of the surface of the point 26 therefore if a hole is to be drilled at point 26 the drill bit can be positioned precisely normal the surface to be drilled preventing the drill bit from being deflected or skipping off of the point and insuring an effective hole is drilled through the material for subsequently receiving a rivet although one embodiment of the invention.