Three settings

Worked example: preferred against required

The sample fair in the judge assigner has six categories and twelve judges with two categories each, plus the rule that no two judges from one school or employer share a panel. With matching preferred, the assigner fills 108 of 108 seats and sends 4 visits to a judge outside their categories.

Switch the same fair to required and it fills 104 of 108, leaving 4 projects short. The first one on the list reads: "P104 Plant growth under LED light: has 2 of 3 judges. Of the 10 other judges, 2 have a conflict with it, 8 do not judge Biology. Only 2 judges can judge it at all under these rules, and the rules ask for 3." The maximum flow check puts the ceiling at 106 seats, a ceiling that ignores the one school rule, so the assigner says the rules might allow up to that many rather than claiming a proof. For this fair, preferred is the better choice: 4 visits outside a category are easier to live with than 4 empty seats.

Expertise tags

Tags are short words a judge enters: soil, robots, water filter. A tag matches a project when every word of it appears in the project's category, flags or title, with plurals folded, so plants matches Plant growth under LED light. Each visit without a match costs 3 points, far less than a category miss, so tags only decide between judges who are otherwise equal. In the sample fair 21 visits match a tag.

Common mistakes

Short panels are explained in how many judges per project, and conflicts in judge conflicts of interest.

Sources

Frequently asked questions

Should science fair judges only judge their own category?

Prefer it, and require it only where the category truly needs specialist knowledge and you have enough specialists. Requiring it with too few judges leaves panels short, and a short panel is worse than a capable judge from a neighbouring field.

What is the difference between categories and expertise tags?

Categories are the fair's divisions of projects, such as Chemistry or Engineering, and a judge picks the ones they can judge. Expertise tags are finer words, such as soil or robots, that the assigner matches against a project's category, flags and title as a tie breaker.

What if a judge can judge anything?

Leave their categories empty. The assigner treats them as able to judge any category, which makes them the most useful volunteers on a tight day.

Can I see which visits are outside a judge's categories?

Yes. The grid marks each one with a note, the comparison of two drafts counts them, and the Rules tab lets you switch between required and preferred and assign again to see the difference.

More guides

Last reviewed 27 September 2026. Judgegrid is not affiliated with any science fair, science fair organisation, competition, hackathon, school, school district or judging software company.