Precisely Set Your Plane Iron or Jointer Knives Depth of Cut in Seconds. Take Trial And Error Guesswork Out Of Plane Iron Adjustment.Magnets secure device to plane bottom during adjustmentsReading: Inch/mm/Fractions - 0.0005"/0.01mm/ 1/128"Accuracy: 0.001"Measuring range: 0-5/32"Super Large Display. Humidity & Dust Resistant.