Rulers

• Rulers, yardsticks and tape measures are part of even the most basic toolkit. Use them for laying out length, width and thickness of stock. Tape measures are best for long beams, but become awkward on long stock. Curved surfaces and changing tensions can affect accuracy. For the finest results use a laser measuring device -- the best are accurate to within 1/4 inch over a span of 100 feet. Ultrasonic measuring devices use sonar beams to measure distance and are less accurate, but some can quickly perform complex measurements such as calculating the volume of a room.
  
  

Squares

• Traditional tools like the framing square still are the most common way to lay out or check the squareness of stock. Framing squares measure 90 degree angles by fit, but by using the scales on both arms woodworkers make complex measurements of other angles. Speed squares are a newer invention, built in the shape of a right triangle. Matching the square to the stock checks both right angles and 45-degree angles. Adjustable bevel squares can be set to any angle for repetitive measurements, and combination squares double as depth gages and levels.
  
  

Levels

• Bubble levels check the slope of foundations, provide a level guide during masonry construction and show whether or not vertical beams are straight. Small bubble levels sliding on a long string can help determine the correct height for setting posts. Even laser levels that mark perfectly straight horizontal lines often have bubble levels built in, to help set up the laser beam projector accurately.
  
  

Calipers

• Calipers measure the thickness of materials and the diameter of rods and turnery. One type, the inside/outside or turner's caliper, measures outside diameter at one end and gives a matching inside diameter setting at the other. Micrometers are more useful for machinists, with results measurable by .001 inch.
  
  

Gages

• Gages include all sorts of common jigs and manufactured tools designed to solve specific and even unusual problems. Many are so simple that woodworkers nearly always make them on the spot. A diagonal stick checks the carcass of a piece of furniture for square corners by measuring the diagonal distances across it. If it is square, the length of both is the same. Winding sticks -- perfectly squared straight sticks in matching dimensions -- check the trueness of a surface. Lay one on each end of the board and sight across them. They will be parallel if the surface is true. Spacing sticks quicken the layout of simple repetitive work like the pickets on a fence. A piece of wood cut to match the gap locates the next picket without the need for guidelines.