this is a yes and no answer. there are more than one ways to calibrate a cat!
You do it in accordance with manuf recommendations to start with; that is essentially permission to turn it on and use it.
Then you calibrate it in accordance with procedures that the machine is compatible with. This woud be your iso 17025 / wada acknowledgement.
then, if you are using it for research etc, you can mess about with the machien to your hearts content and draw up your own procedures and calibration procedures / curves etc to go further, but this is normalllly unreasnoably expensive.
to go back to the gps; most watches are self calibrating to the limits needed (they turn on and receive a signal, perform calcs and give answers, with error checks which will throw out a generic error if not working).
However, if you really want, you can use a gps manufacturers stated '3m' or similar accuracy and start really playing with it. Many people think if you measure twice (at 3m accuracy) divide by 2, you will get 1.5m accuracy. this is between bullpoo and naivety, however there are highly complex statistical analysises that can be done with massive numbers of readings (monte carlo nonsense etc) which can be shown to give results better than 3m - however the cost is axttravagant and you may as well use a better way in the first place. Not a fan of them myself. Normally more bamboozle than fact. and a gift for consultancy fee justification. ooops.