The new international rules and regulations for showing and judging giant vegetables and related crops have been posted here: https://www.pompoenweging.nl/rules and will appear on this website and others soon.
These rules can be freely used by all growers and weigh-offs and may be posted on any website. The GPC is using these rules when they help growers at a GPC event claim a Guinness World Record.
In the document you can see who was involved in making these rules and which resources were used.
All weigh-offs/fairs, etc are strongly advised to use these rules in order to standardize judging.