A second pair of hands

Handing the ruler to someone else does not automatically produce a better number. It trades one set of errors for another, and the trade is only worth it if you brief the second measurer properly first.

What the swap removes

A self-measurer is looking down and back at their own ruler, which foreshortens the scale and shifts where the tip appears to fall - the geometry of that particular bias is worth reading on its own. A second measurer standing beside you, sighting the ruler roughly level, does not have that problem. They also do not have the mild, unconscious motivation to press a fraction lighter or angle the ruler a fraction favourably, which is one of the mechanical reasons a self-measured and a clinician-measured reading tend to diverge even on identical equipment.

What to tell them before they touch the ruler

Four things, in order, and skipping any one of them undoes most of the benefit.

Where the landmark is. The ruler stops at the pubic bone, above the shaft, not on the skin in front of it. If they have never done this, show them once on your own hand pressed to your own body so they feel where "stopped on bone" is different from "stopped on soft tissue."

Which line to follow. Along the top, base to tip, not the underside. The two give different numbers and only one is comparable to anything published.

To keep the ruler parallel to the shaft. Not level with the floor, not level with their eye - parallel to the axis being measured. An angled ruler adds length that is an artefact of the angle rather than anything real.

To press firmly and consistently, then hold it. The pressure needs to be enough to compress the fat pad the same way each time, not tentative because they are new to the task and not eager because they are trying to be helpful.

Have them read the number back to you rather than announcing it, and take three readings the way you would alone, using the median of the three. It helps to walk through the four points out loud once before starting, rather than explaining as you go - a briefing interrupted mid-reading tends to get skipped under the awkwardness of the moment.

The variance a second measurer adds

None of this makes the reading perfect. It swaps your viewing-angle error for an inter-observer one: a person who has taken this measurement once is finding the landmark and the line for the first time, and their first attempt will not be as consistent as a clinician's hundredth. Where two people take the same measurement in a study setting, agreement is good but not exact, which is a useful thing to know before treating a single second-person reading as a ground truth rather than as one more careful estimate.

There is also a state problem worth naming honestly: having another person present and touching the measurement changes the situation you are measuring in, and a reading taken under those conditions is not guaranteed to match one taken alone. If the number looks unusually different from your own solo readings, that is information about the swap, not necessarily about which reading was closer to the truth. Briefing a second measurer this way is a distinct question from what having a partner present does to the state you are measuring, which is worth reading separately since one is about who reads the ruler and the other is about who is in the room.

Where this fits

A second measurer is a way to reduce one specific error, not a shortcut around the method itself, and everything else in the bone-pressed protocol still applies regardless of who is holding the ruler. None of it turns the result into anything other than a length in centimetres with an uncertainty attached - it is not a judgement, and a rating built from a photograph, the kind Penis Rater produces, is answering a different question entirely, as is a human judge's opinion, which carries no ruler and no landmark at all. An AI model reading an image has the same limit for a different reason: there is no scale information in a photograph for it to recover a length from, whoever is holding the phone. If what you actually wanted was that kind of subjective read rather than a distance, Rate Cock is built for it - a second pair of hands with a ruler is solving a narrower and more literal problem than that.