Calibrating application equipment is something many people avoid because they believe it is too time consuming or that the math involved in the process is confusing. Calibration, however, is critical. Applying too much can be bad for the environment, injure the grass, and also wastes money. Applying too little can result in poor pest control and can lead to pesticide resistance. There are several methods that will calibrate sprayers but the no-math method is likely the most simple and reduces the chance of errors.
Munshaw, Gregg, "A No-Math Method of Calibrating Backpack Sprayers and Lawn Care Spray Guns" (2016). Agriculture and Natural Resources Publications. Paper 94.