July Numbers, January Numbers

A client of ours, a retired hydrologist who has given permission for this on the condition that he is not named, has been coming in twice a year since 2015. Once in the second week of January and once in the second week of July, in the same bay, on the same equipment, with the same ball model, for eleven years now.

He did not set out to build a dataset. He started because he could not work out whether he was declining, and every fitting he had ever had told him a single number on a single day, which answered nothing. Two readings a year, dated and with conditions attached, was his own idea and it is the most useful thing in our filing cabinet.

What follows is his six iron. I have his permission to print it and the file is his to withdraw at any point.

The Raw Figures

Two things jump out of that table, and only one of them is about him.

The Seasonal Gap Never Moves

Look at the fourth column. Eight, nine, eight, nine, eight, nine. Across eleven years and a twelve-yard decline in absolute terms, the difference between his January six iron and his July six iron has stayed within a single yard of the same figure.

That is the air, and nothing else. He is not eight yards better in summer. The ball is travelling through thinner, warmer stuff and covering more ground for the same launch conditions, exactly as it should. The consistency of that gap over a decade is, to me, the most persuasive demonstration of the temperature effect I have ever seen, precisely because it comes from one ordinary golfer rather than from a model.

It also means something practical: his seasonal variation is not noise to be smoothed away. It is a stable, predictable, roughly nine-yard shift that he can plan around, and does. He carries one card with two columns.

The Decline Is Real, and Slower Than He Feared

Now the column on the right. Comparing January to January, which holds the season constant, he has lost twelve yards in a decade. That works out at a little over a yard a year, which is entirely unremarkable for a man who was in his late fifties when this started.

What is worth noting is what he believed before the file existed. He was convinced, in 2019, that he had fallen off a cliff, and he arrived that January genuinely upset about it. He had been playing all summer, gone out on a cold morning in January, and lost nine yards from what he remembered.

Of course he had. Eight of those nine yards were the season. His actual year-on-year loss between 2018 and 2020 was two yards.

Without dated sheets there was no way for him to know that, and every instinct he had was pushing him toward a wrong conclusion. He had come in intending to buy a lighter shafted set, which would have been a reasonable purchase for a genuine nine-yard decline and was an unnecessary one for a two-yard decline plus a January morning.

What This Means If You Are Fitted Once

A single session gives you one point. One point cannot show a trend and it cannot separate a seasonal effect from a personal one. It can still be extremely useful for spacing and for specification, which is most of what people come in for, but on the question of "am I losing it" it is close to silent.

Two points a year apart in the same month give you a great deal more. Two points six months apart give you the seasonal gap, which is a different and also useful thing. Both, repeated, and you have what he has, which is the ability to tell whether an unwelcome round was information or weather.

Nobody needs to be fitted twice a year, and I want to be careful not to turn this note into a sales pitch for a service almost nobody requires. What most players need is far cheaper: write the date and the temperature on whatever numbers you already have. That is free, it takes ten seconds, and it is the difference between a figure that can be compared and one that cannot.

Two Smaller Findings From the Same File

His spread has widened more than his distance has fallen. In 2016 his six iron block covered fourteen yards. In 2026 it covers twenty-three. That is the more consequential change and it is invisible in any conversation about distance. It is also the reason his specification changed in 2023 toward a more forgiving head, which was a decision made on the spread column rather than on the carry column.

The July readings decline slightly faster than the January ones. Fourteen yards lost in July against twelve in January over the same period. This makes sense: the percentage effect of the air is constant, so as his baseline drops, the absolute size of his summer bonus drops with it. A nine-yard gap on a hundred and seventy-six yard club is a smaller proportional gap than nine yards on a hundred and sixty-five. Small, but the file shows it, and it is the kind of thing that only emerges from years of consistent conditions headers.

The Point of Keeping Records

He said something on his last visit that I have thought about since. He said the file had not made him play better, and that he had not expected it to. What it had done was stop him from making three or four expensive decisions based on a bad morning.

That seems to me the honest case for measurement of any kind. It rarely improves the thing being measured. It reliably improves the decisions made about it.