When laying out the footings, the author determines diagonal measurements using the rise/run function on his construction calculator, then refers to those measurements to verify that corners are square. The stretched string on the right-hand side of the photo indicates the outside edge of the first set of footings.
Figure 2. Footing forms are fastened together at the corners with duplex nails; 16-inch metal spreaders keep the sides properly spaced.
A single crew member can level the staked forms using a rotary laser. The receiver included with the Stabila LAR250 kit used by the author indicates distance from grade in 1/16-inch increments.
Companies that do production foundation work may want to consider the Max cordless rebar tier ( maxusacorp.com), which automatically makes a tie in less than a second.