Everything We End Up Explaining Twice a Week
None of this is secret and none of it requires a session to understand. It is here so that when you sit down in the bay you already know what the numbers on the screen are telling you.
If you only read one section, read the one about proportional correction. It causes more bad gapping decisions in this valley than everything else combined.
Air Density Is the Only Thing That Actually Matters
Golfers talk about altitude, but altitude is a proxy. What changes the flight of a golf ball is the mass of air in each cubic foot it travels through. Thinner air means less drag and less lift, and the two do not cancel out — drag wins, so the ball goes further.
Three things set air density, and elevation is only the first of them.
Elevation
The dominant term. Air pressure falls roughly exponentially with height. At our studio floor the pressure is around 85 percent of what a sea-level course sees. Up at the lake courses it drops to roughly 79 percent. That difference alone moves a mid-iron by more than a full club.
Temperature
Warm air is less dense than cold air at the same pressure. A forty-degree change between a dawn tee time and a late afternoon finish is entirely normal here in June, and it is worth several yards on a mid-iron and considerably more on a driver.
Humidity
Counter-intuitively, humid air is slightly less dense than dry air, because water vapour molecules are lighter than the nitrogen and oxygen they displace. The effect is genuinely small — a yard or two — and in our climate it works against us rather than for us. It is worth knowing about and not worth planning around.
The Correction Is Proportional, Not Flat
This is the one that costs people strokes. When a golfer learns the ball goes about seven percent further here, the instinct is to convert that into yards for one club and apply the same number of yards to the whole bag. Seven percent of a 300-yard drive is 21 yards. Seven percent of a 90-yard wedge is six.
Apply "add twenty yards" to your wedges and you have invented a distance you cannot hit. Apply "add six yards" to your driver and you have understated it by fifteen. Either mistake produces a set with a hole in it, and the hole always turns up at the worst possible moment, which is a par three over water.
Rule of thumb: think in percentages, never in yards, until the very last step. Convert each club separately and write the result down. Doing it in your head on the tee is how the mistake gets made.
Carry Is Yours, Total Distance Is Rented
A launch monitor reports both, and total is the bigger number, so total is the one people remember. It is also the one that changes most between April and August on a high-desert course. Fairways that are soft in spring and concrete in August will change your total by twenty yards without your swing changing at all.
Carry is a function of how you struck the ball and what the air did to it. Nothing about the ground is in it. That is why every column on our sheets is a carry figure and why we will politely refuse to write a total distance next to a club name.
Reading the Spread Instead of the Average
The single most useful number on a launch monitor session is not the average carry. It is the distance between the shortest ball in the sample and the longest, once you have thrown out the two extremes at each end.
A golfer whose seven-iron averages 165 with a spread of eight yards needs different gapping than a golfer whose seven-iron averages 165 with a spread of twenty-six. The first golfer can run four-yard gaps and be fine. The second cannot tell two adjacent clubs apart on the course no matter how carefully the lofts are set, and would be better served by a shorter set with wider gaps.
Descent Angle on Ground That Does Not Yield
Our greens in midsummer are firm. A ball arriving at a shallow angle will release regardless of how much spin it carries, and a ball arriving steeply will stop even with moderate spin. That makes descent angle a more useful thing to fit for here than spin rate, which is the opposite of what most fitting content assumes.
In practice this pushes long-iron and hybrid decisions towards higher-launching configurations than a sea-level fitter would choose, and it pushes wedge decisions towards less bounce than a golfer from a wet climate would expect.
What a Shaft Actually Changes, and What It Does Not
A shaft change is a good tool for adjusting launch height, spin, timing and feel. It is a poor tool for adding distance. Golfers arrive expecting the reverse.
Most of the distance gains people attribute to a new shaft come from a strike that moved closer to the centre of the face, and the shaft helped that happen by making the club easier to time. That is a real benefit, but it is worth being honest about the mechanism, because it also explains why the same shaft in someone else's hands does nothing at all.
Or We Can Just Measure It
Reading about air density is useful. Watching your own eight-iron produce three different numbers on one sheet is more useful.