Calibration makes your instruments more accurate and useful
Sailing instrument calibration systems is necessary to make displayed information correct and useful. Instrument systems use sensors to measure primary environmental factors (boatspeed, wind, heading, position, heel and others), possibly combine them, and display the results. Calibrations adjust for things like boundary layer (paddlewheels), upwash (masthead units), and installation variables such as compass deviation or sensor misalignment. Almost all instrument systems, including stand-alone types, offer some kind of input calibration.
Calibration is not all that difficult, requiring a few dedicated hours under good sailing conditions. Instrument calibration should not be combined with rig tuning or sail skepsis – it should have its own day. You will adjust boatspeed, heading and apparent wind to deliver a steady and reliable wind direction and current.
There is also an automated calibration helper application, DeWiggler, which makes the job easier and faster.
Setting up and maintaining an instrument system is not entirely or even mostly about the technical process. There are also important organizational structures to be created and maintained as well. Most calibration dysfunction and nightmare stories are related to social issues and not the hardware.