Pipes can be measured using the measuring reference surface with the V shaped groove 6-LINE AIR BUBBLE TUBES 1/100 gradient (1min slope) 2/100 (2min slope) measuring Magnifying lens for easier us Being phosphorescent, the device draws on light from well-lit places to emit light for a few minutes in darker applications. Very convenient with its own accuracy adjuster. SPECIFICATIONS Hardened extruded Aluminium alloy Alumite clear painted finish 6-line acrylic horizontal air bubble tubes with lenses 6-line acrylic vertical air bubble tubes SENSITIVITY / ACCURACY Sensitivity 0.35mm/m=0.0201˚ Accuracy: Within ±1.00mm/m±0.0573˚