How slope-adjusted yardage works

The triangle behind every slope reading

Picture a right-angled triangle between you and an elevated flag. The laser measures the long side, the line of sight distance from the device to the flag. A built-in inclinometer measures the angle between that line and level ground. With those two numbers, basic trigonometry gives the other two sides: the horizontal distance along the ground (distance multiplied by the cosine of the angle) and the height difference (distance multiplied by the sine of the angle).

Every slope laser solves this triangle in a fraction of a second. It is pure geometry, so all devices should agree on the height difference if they measure the same distance and angle. Where they differ is the next step: turning height into a 'plays like' yardage.

A worked example in yards and metres

Say you laser a flag 150 yards away along the line of sight, and the device reads an angle of 8 degrees uphill. The horizontal distance is 150 x cos 8°, which is about 148.5 yards. The height difference is 150 x sin 8°, about 20.9 yards, which is roughly 19.1 metres or 63 feet. That is a big climb, similar to a green perched on a steep bank.

Notice that the horizontal distance barely changes. Even at 15 degrees, a very steep shot for golf, it only falls by about 5 yards. The height difference grows quickly, and that is what makes the shot play longer or shorter. You can run your own numbers with our rangefinder maths tool, which converts between yards, metres and feet.

Try the rangefinder maths tool →

Why plays-like is not the horizontal distance

If you only used the horizontal distance, an uphill shot would look slightly shorter than the line of sight, which is the opposite of what golfers feel. The ball has to climb, so it lands earlier on its descent and travels less far forward before it meets the higher ground. Downhill, the ball keeps falling past the point where it would have landed on level ground, so it travels further.

Makers model this with their own formulas, usually starting from the height difference and adding or subtracting a share of it to the distance, then adjusting for typical ball flight. Some add more inputs. The Mileseey GenePro G1 listing, for example, says its SmartSlope also uses temperature and humidity. Bushnell, Nikon, Shot Scope and Voice Caddie each describe their own slope technology. That is why one laser might say 158 and another 161 for the same shot. Neither is wrong; they use different models of ball flight.

• Same for every device: line of sight distance, angle, horizontal distance and height difference.
• Different by brand: the plays-like figure, because each maker uses its own formula.
• Different by golfer: how your own ball flight responds, since a high, spinning iron shot and a low runner react differently.

How to use slope numbers well

Slope works best as a learning tool in practice rounds. Laser the target, note the actual distance and the plays-like figure, then pay attention to where your ball finishes. After a few rounds you will start to judge elevation by eye, which you will need in competitions when slope must be off. Lasers with a dual display, such as the Bushnell Tour V7 Shift or Nikon Coolshot 20i GIII in our slope rangefinder guide, show both figures together, which makes this kind of learning easier.

1. 1

   Laser the target and read both the actual and the plays-like distance.

2. 2

   Pick a club for the plays-like number and note the result.

3. 3

   In the next round, guess the adjustment before you laser, then check.

4. 4

   Keep the habit going so you can judge elevation without the slope function.

Note:Hold the laser steady and aim only at course targets. Makers describe golf lasers as eye-safe Class 1 products, but they still warn against pointing them at people or looking at the sun through the optics. Read your manual.

Slope and the Rules of Golf

Under Rule 4.3, you may use a device to measure distance, but you must not use it to measure elevation changes during a round. A slope laser is allowed in competition provided the slope function is switched off. Our explainer on whether rangefinders are legal covers the detail, including how a Local Rule can ban distance devices completely.

For competition golf, consider how you turn slope off. External switches, as on the Bushnell Tour V6 Shift, are the clearest. Our rangefinder buying guide notes how each model handles this.

Frequently asked questions

Why does my laser say a downhill shot plays shorter than the actual distance? Because the ball keeps falling past the point where it would land on level ground. The device subtracts part of the height difference to reflect that.

Why do two slope lasers give different plays-like numbers? The geometry is the same, but each maker uses its own formula to convert height into a plays-like distance, and some add temperature or other inputs.

Is the horizontal distance the same as the plays-like distance? No. The horizontal distance is pure geometry and changes little with angle. The plays-like figure adds the effect of height on ball flight.

Can I use slope in a club medal? No. Slope must be switched off in competition under Rule 4.3, though the device itself can still be used for distance.