Method
A single reading
One careful reading gives you a figure to the nearest half-centimetre and nothing about your error; it is a start, not a result.
One reading is a number. It is not yet a result, because a result needs an error bar and a single figure cannot supply its own.
What one reading actually gives you
Take the measurement carefully, the way the studies do it, and you get a real figure: bone-pressed, to the nearest millimetre, taken at a stated state. That much is genuine information. What it does not tell you is how much that figure would move if you took it again five minutes later, with the same care, on the same body.
Pressure, angle, and where exactly the ruler seated against the bone all vary slightly between attempts even when technique is good. A second reading routinely lands a few millimetres from the first for reasons that have nothing to do with anatomy changing. One number cannot distinguish "this is precisely where I sit" from "this happened to be a high or low draw."
Why this matters more near round numbers
The temptation is to treat a single reading as settled, especially when it lands on a number that feels meaningful. That is exactly the reading most worth distrusting, because confirmation bias does its work quietly: a figure that confirms what you expected gets accepted without a second look, and one that does not gets remeasured until it does. A number you have only taken once has not been tested against itself yet.
What to do instead
The fix is not more care on a single attempt, it is repetition: three readings in one sitting, and a stated way of combining them, which is what turns a figure into something you can attach an honest uncertainty to. Until then, a single reading is best written down as provisional, with the date and method next to it, rather than treated as a fixed fact about yourself.
That discipline is also what separates this kind of number from the kind that other sites deal in. A rating from a photo, the sort Rate Cock, an AI model at AI Penis, or a human panel at Rate Penis might produce, is a single judgement by design and belongs to a different category of number - worth keeping distinct from a physical one - and so do the aggregate scores Penis Rater builds from many of them. A length in centimetres, by contrast, is exactly the kind of number that gets more trustworthy the more carefully you interrogate it, and the first step is simply not stopping at one.