When determining the time deviation the watch must always be in the same position and at the same temperature (unless you want to determine the effect of temperature on the rate deviation).
Beneath the influence of temperature on the rate deviation one measures also the influence of the location of the movement on the rate deviation. So the rate of wristwatches is measured in different locations over a certain period of time lying with dial up, lying with dial down, standing with crown at the right, standing with crown at the left, standing with crown above, standing with crown below. The measurement series of the different positions are then compared.
At the chronometer certification watches with a particularly low rate of variation are awarded with a certificate from an official source and obtain the title “chronometer”.