What happens if I use green-reading materials during a round?

You can use green-reading materials, but they're strictly limited. Detailed putting green maps must meet size and scale limits under Rule 4.3a/1, and a Committee can ban them entirely with Model Local Rule G-12. Breaking the rule costs you the general penalty — two strokes in stroke play or loss of hole in match play — and a second breach gets you disqualified.

What counts as a green-reading material

Green-reading materials are any written, printed, or digital aids that help you read your line of play on the putting green. This includes detailed green maps showing slopes, contours, and break percentages, whether on paper or a phone app. The rule also covers any similar electronic or digital materials you might consult during the round. Your own notes from previous rounds are fine — those are considered information gathered before the round, which Rule 4.3a(3) explicitly allows.

The size and scale limits

Interpretation 4.3a/1 puts a cap on how detailed these materials can be. The idea is that reading a green should remain an essential skill, not something a map does for you. The exact size and scale limits are technical specifications the Committee can enforce, but the practical takeaway is: pocket-sized books with general green diagrams are usually okay; large-scale, highly detailed topo maps that show every subtle break are not. If you're unsure whether your material passes, ask the Committee before the round.

When the Committee bans them entirely

A Committee can adopt Model Local Rule G-12, which modifies Rule 4.3a to prohibit all green-reading materials for strokes made from the putting green. If G-12 is in effect, you cannot use any written or digital material to help read your line on the green — not even a simple sketch. Always check the Local Rules sheet or notice board before you tee off. If G-12 applies and you pull out a green book, you're in breach.

Exceptions that change the answer

• Model Local Rule G-12 is in effect → All green-reading materials are prohibited for strokes from the putting green, regardless of size or scale.
• You use your own notes from previous rounds → That's allowed under Rule 4.3a(3) as information gathered before the round.
• You use a club as a plumb line to gauge slope → That's specifically permitted under Interpretation 4.3a(1)/1, but bubble levels, bottled drinks as levels, or weighted strings are not allowed.

Frequently asked questions

What's the penalty if I use a prohibited green book?

First breach: general penalty — two strokes in stroke play, loss of hole in match play. Second breach: disqualification. The penalty applies per round, not per hole.

Can I look at a green map before I putt, then put it away?

No. Consulting a prohibited material at any time during the round for a stroke from the putting green is a breach, even if you don't have it in hand when you make the stroke.

Are handwritten notes from today's round allowed?

No. Rule 4.3a(3) prohibits processing or interpreting playing information from the current round. Notes you make during the round about green slopes count as interpreting current-round information.

Can my caddie use a green-reading book and tell me the line?

No. If the material is prohibited for you, it's prohibited for your caddie too. Your caddie's breach is treated as your breach under Rule 10.3c.