
I've always used spirit levels and very rarely my iPhone to level things, but with both you don't have a way to 'set' the spirit level. This allows you to set the zero plane anywhere you like, making finding rafter angles 10 times easier than digging up a combination angle and measuring.

π Kapro 905-41-24 24-Inch Level Tool - Premium Bubble Level with Shockproof End Caps, Superior Accuracy & Visibility, Optivision Red and Plumb Site Dual View Vial, Condor Spirit Level
10 Review

π΅ IRWIN Tools Bullseye Level (1794487) - Blue
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Laser level HiLDA 4D/16 set 4
44 Review

π SKIL 24-Inch Digital Level - LV941901
8 Review

Kapro - 353 Professional Ledge-It Try & Mitre Square - For Leveling And Measuring - Features Stainless Steel Blade, Retractable Ledge, And Etched Ruler Markings - 12 Inch
23 Review

TV bracket Kromax DIX-18 black
52 Review

π Johnson Level and Tool 400EM-S 12-Inch Heavy Duty Metal Combination Square for Professionals, with Inch/Metric Measurements, Silver - 1 Square
8 Review

β Stainless Steel L-Square, Size 3-Inch x 4-Inch, Zona 37-434
8 Review