What do launch monitor ball numbers mean, and which are measured?

Two kinds of ball number

Every launch monitor reports a handful of ball numbers, but they aren't all the same kind of number. Some are measured: the unit actually sees them in the first moments after impact. The rest are calculated: the software works them out from the measured ones. Foresight puts it plainly in its guide to ball data. Ball speed, total spin, launch angle, azimuth and spin axis are the measured launch conditions, and together they "determine the ball trajectory, peak height, descent angle, carry and total distance".

That matters more indoors than anywhere else. In a simulator the ball hits the screen about 2.5m after impact, so nothing can watch it land. Carry and total distance on screen are always the software's prediction from the launch. TruGolf's LaunchBox manual is a good example of a maker spelling this out: it lists ball speed, launch angle, back spin, side spin and side angle as measured, and carry, total, offline and roll as calculated.

So when two launch monitors disagree about your 7-iron, the place to look is the measured numbers. If ball speed, launch and spin match, the carry will too.

The measured numbers

Ball speed

How fast the ball leaves the face, in mph. Foresight calls it "the main component in generating distance". It is the number every unit measures best, radar or camera.

Launch angle

The angle the ball climbs at, in degrees, measured from the ground. Foresight defines it as "the initial vertical angle of ascent relative to the ground plane". FlightScope calls it vertical launch angle.

Launch direction

Which way the ball starts, left or right of your target line, in degrees. Foresight calls it azimuth, FlightScope horizontal launch angle, TruGolf side angle and Garmin launch direction. They are the same thing. Because it is measured against the unit's target line, a launch monitor that isn't lined up properly reports every shot as a push or a pull. Placement and alignment covers how to set it.

Spin rate

How fast the ball spins, in revolutions per minute (rpm). Some units report it as one total figure. Others split it into back spin, which gives lift and makes the ball stop, and side spin, which makes it curve. Square Golf, Uneekor and TruGolf show both parts.

Spin axis

The tilt of the spin. Foresight's guide says that when the axis tilts left, looking down the range, the ball moves from right to left, and when it tilts right the ball moves left to right. Zero means no curve. Units that show back spin and side spin instead are describing the same thing in two numbers.

The calculated numbers

• Carry: how far the ball flies before it first lands. Foresight: "the total distance of flight produced by initial launch condition".
• Total distance: carry plus bounce and roll. This also depends on the ground the software models, so it changes with the course and settings.
• Apex or peak height: the highest point of the flight.
• Offline: how far left or right of the target line the ball finishes. Garmin calls it deviation distance.
• Descent angle: how steeply the ball lands. Not every unit reports it; the R50 doesn't list it.

Garmin's R50 manual adds a useful warning: if shots fly longer than expected, check the ball flight conditions setting, which models altitude and conditions. The same launch can give different carries at different settings.

How radar and camera units read the ball

A camera unit sits beside the ball and photographs it at impact, so it sees ball speed, launch and spin directly from the ball's markings. That's why Garmin, SkyTrak and TruGolf all ask you to set the ball with its logo or a marked line facing the unit. Square Golf goes further: with its patterned balls, back spin and side spin are measured; with a normal ball they are estimated.

A radar unit sits behind you and tracks the ball as it flies away. Speed and launch are easy for it. Spin is harder indoors, because the ball only flies 2.5m before the screen stops it. The makers each deal with this in their own way:

• FlightScope Mevo Gen2: the manual says aluminium stickers or Titleist RCT balls are "required for accurate spin measurements" indoors. Outdoors, no sticker is needed.
• Garmin Approach R10: Garmin says Titleist RCT balls give "up to a 30 times more accurate reading of spin rate".
• Full Swing KIT: Full Swing says RCT balls give a stronger radar signal "to support indoor spin measurement".
• Rapsodo MLM2PRO: measured spin and spin axis need both the Callaway RPT ball and a Core membership, per Rapsodo's user guide.

The table below lists what each unit we sell measures, in its maker's words, and what it needs indoors. Balls and tracking stickers goes through each one in detail.

How I'd read your numbers

1. Start with ball speed. It tells you more about the strike than anything else.
2. Then launch and spin together. A low launch with high spin, or a high launch with very low spin, usually explains a short carry.
3. Then launch direction and spin axis. The first tells you where it started, the second how it curved.
4. Treat carry as the result of the three, not a separate measurement.

For what the club was doing to cause those numbers, see club data explained.