Before picking a men's hair system, read the three answers still growing on the sides of your head

Most men start this by hunting for a photo. Something from a few years back, hair still doing its job, held up next to a screen or a color ring. That photo is where the trouble starts. Three years changes the grey at the temples, thins the sides, and pushes the bald area back far enough that the old picture is describing somebody else's head.

The reference that works is still attached. The hair on the sides and around the back hasn't gone anywhere, and it carries every answer a supplier needs: how wide the base has to be, how much hair gets knotted into it, and which shade out of 120-something comes closest. Three answers, one place to look, no photo album involved.

Where the coverage has to stop

Base size gets treated like a hat size. It isn't. A men's hair system has to cover a gap, and the gap is the distance between the hair that's still there.

Two men can share a head circumference and need completely different bases. One has a coin-sized spot at the crown, the other is bare from the hairline back to the top of the nape. Same tape measure, two different pieces of lace. A catalog runs from roughly 5 x 7 inches at the small end, through 6 x 8 and 7 x 9, out to 8 x 10 at the top, and most stock sits somewhere in the middle of that range because the middle covers the most buyers.

The line where the hair stops is also a moving line. It creeps back a bit most years. Order a base that ends exactly on today's edge and there's a strip of scalp sitting just past it by next winter. Land the base a little past the thin zone instead, onto hair with enough body to hide a seam. A base that stops right at the thin edge puts the seam in the thinnest hair on the head, which is the one place on the whole head where a seam has nowhere to hide.

That margin is also the reason the trace has to be taken flat. Cling film, tape over it, marker along the hairline on all four sides, then peel and lay it on a table. A piece traced following the curve of the skull comes back bigger than the head it was measured from.

How much hair goes on top of it

Density has a test that takes about five seconds. Push the hair on the side of the head flat against the scalp with a comb and look at how much scalp shows through. Some, a lot, barely any. That's the reference. Whatever the sides do, the top should do something close to it.

The most common mistake is a top that's thicker than the sides it's sitting next to. A man in his fifties with visibly thinning sides doesn't read as a man in his fifties when the crown above them carries full density. The hair around the piece is the only comparison anyone looking at the head has. Grey shifts the same setting. White and silver bounce far more light than dark brown, so a knotting that looks ordinary in a dark shade looks like a helmet in a white one. Grey and white units usually want one step down from whatever the number on the box says.

Which shade, and why the temple is the one that counts

Take the reading at the temple. Grey shows up there first on most heads, and the back of the skull is usually the last place to go. A match pulled from the back of the head comes out too dark within a year.

Read it in daylight too. Bathroom bulbs and warm salon lighting push everything warm, and a shade picked under either one turns brassy the first time it hits an office window or a parking lot.

Two values do the work inside those 120-plus shades. Grey percentage, which runs from about 5% up to 90%, is what "salt and pepper" means once it becomes a number. Tone is where matches fall apart. Warm brown knotted next to cool grey hair on the sides goes orange in the sun, and no amount of styling covers it.

Then there's the part the sides can't tell you. Grey only moves one direction, so a unit matched perfectly to today's temples is a step too dark eighteen months from now. Most orders that age well were made a step greyer than the sides read on the day.

What the shelf can't do with grey

Here's the awkward part of that reading. The sides might be asking for human grey, and human grey doesn't sit still on a shelf. The toner fades, the bleached base underneath starts showing through, and the piece drifts yellow somewhere in the three to six month range of warehouse time. That's why grey in a stock catalog is nearly always synthetic. Modacrylic and heat resistant fiber hold a white for years and read clean in daylight.

Human grey and yak hair grey come through custom production instead. Yak grows grey on its own, so there's no bleach and no toner in it waiting to fade, and the texture runs coarser than fine European hair, which sits better next to mature grey. A factory running those is landing around 40 days, against the 8 to 12 weeks the rest of the industry quotes.

What to send with the order

• Photos of the temple, the side and the back of the head, taken in daylight, no flash.

• A flat trace of the scalp outline, with the hairline marked on all four sides.

• A small snip of hair from the side, if a color ring isn't on hand.

• The two numbers the sides suggested: grey percentage and how much scalp shows through.

Stock covers the middle of all three settings and ships in days. Custom covers the ends of them, which is where a lot of men actually are, especially once grey is involved.

The photo from five years ago is a nice picture. It isn't a spec sheet.