The international IRC rating rule has always been a self-measurement system, and official measurement is not a rule requirement unless the boat needs an Endorsed IRC certificate. The IRC Rating Authority takes great care in checking the data supplied, even for standard certificates. However, there is the option of having the data taken by a trained measurer and the owner can then go racing safe in the knowledge that their rating is based on accurate data rather than, for instance, standard hull data.
There is a network of individuals around the world, approved by their relevant local IRC Rule Authority, available to weigh and measure boats for IRC rating. The IRC Measurement Manual is a comprehensive guide to help ensure good and consistent measurement practice by IRC measurers. It includes advice on the general role of the measurer; equipment and techniques; issues to be aware of, and methods for measuring specific data. There are also appendices covering IRC Endorsement, bulb weight, list angle for moveable and variable ballast, and measurement of foils.
The manual has recently been updated with additional information and is available on the IRC website: ircrating.org/irc-certificate/measurement.