What your launch monitor measures, and what it guesses

Two numbers on the same screen can have very different trust behind them. How to tell a measured value from a calculated one, and why a coach should weigh them differently.

A launch monitor shows twenty numbers in the same font. They are not equally trustworthy. Some were measured by a sensor. Some were worked out from other numbers. A few are close to a guess. If you are going to change your swing because of a number, it helps to know which kind it is.

Measured, calculated, estimated

Measured means the device saw it. Radar units measure ball speed and club speed directly. Camera units measure launch direction and, on the better ones, spin from the ball itself.
Calculated means it was derived from something measured. A radar that cannot see the ball spin has to work spin out from the way the ball slows down, so it is a model, not a reading.
Estimated means the device is inferring a number it cannot see at all. Face angle and dynamic loft are the usual examples on some units; the manufacturer's own manual often says so, in small print.

Which number falls into which bucket depends on the device. Check the manual for yours rather than trusting a forum post, ours included.

Why it matters for practice

Face angle and club path decide the curve of the ball. If face is an estimate, a "face 3° open" reading is a hint, not a fact. Ball flight, on the other hand (where it started, how far it went, which way it curved), is measured on almost every device, and the ball flight laws let you work back to what the face and path must have been.

Range balls make it worse. Worn, low-compression range balls spin and fly differently, which skews anything a monitor derives from ball speed and spin. Your carry with a range ball will usually be a little shorter than with your own.

What we do about it

Swingman's coach knows which numbers your device measures and which it derives, and weighs them accordingly. A fault only becomes your focus when it shows up across shots and sessions, and each finding says how confident it is and why. If the evidence rests on an estimated number, it says that too.

If you are choosing between monitors, ask of each one: which of the numbers I care about does it actually measure? That answer matters more than the price.

Questions or a correction? Get in touch.