Can I use a non-official yardage book or course map?

Yes, you can use a yardage book or course map that isn't the official one. Rule 4.3 allows any distance or directional information, but the material must not measure elevation changes, interpret data to suggest a line of play or club, or exceed the size and scale limits for putting-green maps.

What the rule actually permits

Rule 4.3a(1) lets you get distance and directional information from any source — a printed book, a phone app, a rangefinder, or a hand-drawn sketch. The rule does not care who published it; it cares what the material does. As long as it only gives you raw yardages and general direction, it is allowed. What crosses the line is any feature that "interprets" the information for you. A book that colors a landing zone to suggest the best target, an app that recommends a club based on your current lie, or a map that shows elevation gain or loss are all prohibited because they artificially reduce the judgment the game demands.

Putting-green maps have extra limits

Interpretation 4.3a/1 caps the size and scale of detailed green-reading materials. Even a perfectly legal yardage book becomes illegal on the putting green if its green diagrams are larger or more detailed than the allowed scale. A Committee can go further and adopt Model Local Rule G-12, which bans all green-reading materials entirely. Check the local rules sheet before you pull out a detailed green map.

Pre-round notes are fine; live processing is not

You may write down or print anything before the round — yardages from previous rounds, club selections that worked, swing thoughts — and consult them during play. Rule 4.3a(3) explicitly allows using information gathered before the round. What you cannot do is record data during the round (like actual carry distances) and then have a device or app crunch those numbers to give you a club recommendation later that same day.

Exceptions that change the answer

• Committee adopts Model Local Rule G-12 → All green-reading materials are prohibited, even those that meet the size and scale limits.
• Committee adopts Model Local Rule G-5 → All distance-measuring devices are prohibited, but printed yardage books remain allowed.

Frequently asked questions

Can I use a yardage book I bought from a third-party vendor?

Yes. The Rules do not distinguish between official and unofficial publications. Any book that only provides distances and general direction is permitted.

What if my yardage book shows elevation changes with color coding?

That is not allowed. Measuring or displaying elevation changes is explicitly prohibited under Rule 4.3a(1).

Are there limits on how detailed the putting-green diagrams can be?

Yes. Interpretation 4.3a/1 limits the physical size and scale of green maps. If the diagrams exceed those limits, the material is non-conforming for use on the putting green.

Can I write my own yardages in a notebook during the round and use them later that day?

You may record information for use after the round, but you cannot process or interpret playing information from the current round to help you during that same round.