Is a rangefinder legal in competition? (The slope rule, simply)

Yes — in most competitions a rangefinder is allowed, but only for measuring distance, and the slope feature must be switched OFF. Use slope in a counting competition and you risk disqualification. Toggle it off, check the notice board for any Local Rule banning devices, and skip the extra 'advice' features. That's the whole rule in one breath; here's the detail, because the nuance is where golfers come unstuck.

The default rule

Under the Rules of Golf, distance-measuring devices — lasers and GPS alike — are permitted in most competitions by default, but strictly for measuring distance. There's an important subtlety here that the 'is it legal?' framing misses: a DMD's legality isn't fixed in the device, it's set by the competition. The default position allows plain distance measurement, but a committee can switch that allowance off entirely with a Local Rule. So the honest answer is 'usually allowed, unless the notice board says otherwise', and the feature that most often crosses the line is slope.

Slope must be off

Slope is the function that adjusts a yardage for uphill and downhill — it tells you a flat-150 shot 'plays like 162' up the hill. That's reading more than plain distance, which is why it falls foul of the rules in a counting competition. The fix is simple: slope switched OFF. Every decent modern rangefinder has a toggle, and the better ones — like the Bushnell Pro X3+, which also factors temperature and altitude into its 'plays-like' number — show an external indicator (a coloured ring or a sliding switch) so a playing partner or official can see at a glance that slope is disabled. That external tell matters: it's the difference between your word and visible proof. Learn where that switch is before your first medal, not on the first tee with a card in your hand. Crucially, owning a slope-capable device is fine — you simply mustn't have the function active during a counting round.

When slope IS allowed

It's worth stating plainly, because 'slope is illegal' is the lazy shorthand and it isn't quite true: slope is disallowed in competition unless a Local Rule specifically permits it. Some societies, casual competitions and friendly fourballs explicitly allow slope to keep pace of play up, and in those it's perfectly within the rules to leave it on. The principle to carry round is that the committee, not the gadget, decides — so the safe habit is to assume slope-off for any counting competition and only switch it on when you've confirmed the format allows it. For everyday social golf, of course, use whatever helps; this is purely about counting rounds.

Laser or GPS — does the device type change the rules?

Not in the way people assume. The rules treat lasers and GPS units the same: both are distance-measuring devices, both are allowed by default for distance only, and both fall foul of the same restrictions on slope and 'advice' features. A GPS watch or app isn't somehow safer than a laser, and a laser isn't more suspect than a watch — what matters is the function being used, not the form factor. The one practical edge a laser has in a competition setting is the visible slope-off indicator the better units carry; a phone app's settings are buried where nobody can see them, so if you play a lot of medals a laser with an external tell is the easier device to demonstrate you're playing within the rules. Whichever you carry, the obligation is the same: distance only, slope off unless permitted, no wind or club advice.

Two wrinkles that catch people out

First, an individual competition or club can introduce a Local Rule banning DMDs entirely — 'usually allowed' isn't 'always', and some traditional events still prohibit them outright, so check the notice board rather than assume. Second, features beyond plain distance and slope — wind speed and direction, club recommendations, 'auto' advice modes — are generally not permitted in competition even with slope off, because they stray into giving advice the rules reserve for you and your caddie. A device that does plain distance, with slope you can visibly disable, is the safe bet. I make the wider case that slope is overhyped anyway — most amateurs would play better leaving it off and learning their stock numbers.

The safe setup

A plain distance reading is fine in the vast majority of comps. The pre-round routine is three steps: switch slope off and confirm the external indicator shows it's disabled; check the notice board for any Local Rule banning devices; and don't use the wind or club-advice features. An accurate, cleanly slope-toggling unit like the Precision Pro NX10 keeps you both confident and within the rules without paying flagship money. If you're still deciding how much to spend in the first place, how much to spend on a rangefinder is the sensible starting point, and the full field is in our best rangefinders guide.

Who should worry about all this? Really only golfers who play counting competitions — medals, knockouts, club championships, anything that returns a card for handicap or a trophy. If you only ever play social golf, none of it applies: leave slope on, use whatever features help, and enjoy the gadget. Who should buy with the rules front of mind? Anyone who plays regular medals should choose a device with a clean, obvious slope toggle and an external indicator from the off, rather than buying on price alone and discovering on the first tee that they can't prove slope is disabled. Get that one feature right and the rules become a non-issue: switch off, confirm, check the board, and play.