The measurement card

This is not a fourth explanation of how to measure. It is a card: one line per rule, so the whole protocol is checkable at a glance without re-reading the reasoning behind each piece. Each line links to the post that explains why the rule exists, if the why is what you need.

The order below follows the order a session actually runs in: confirm state first, then length, then girth, then the repeats, then the record. Running through it in that order once, before the first reading rather than after, is the entire point of having it on one page - a rule you remember halfway through a session is a rule you apply inconsistently, and inconsistency is what this whole site exists to remove from a number.

State

• Full erection, not "mostly" - firmness changes the reading enough to matter.
• Same time of day across repeat sessions where possible - it removes one variable you cannot otherwise control for.
• Standing, matching the position most published studies use - posture affects the fat pad and the reading.

Landmark and line, for length

• Ruler pressed firmly to the pubic bone, not resting on skin above it - pressure is the largest single source of self-measurement error.
• Clear the base of hair before pressing - hair can stop the ruler short of bone, inconsistently.
• Along the dorsal surface, base to tip, not the underside - the underside gives a longer number that compares to nothing published.
• Ruler parallel to the shaft's own axis, not to the floor - an angled ruler adds length as an artefact of the angle.
• Read where the tip reaches, ruler resting alongside rather than pressed into the glans - pushing in compresses tissue and shifts the mark.

Site and tension, for girth

• Midpoint of the shaft, the conventional site - girth varies enough along the shaft that the site has to be fixed.
• Tape laid onto the skin, not pulled round it - pulling drags skin and changes the circumference traced.
• Steadying hand held at the base, away from the site - a nearby grip compresses tissue and reads the girth low.
• Snug, meaning flat against the skin with no gap and no indentation - tighter reads low, looser reads high.

Repeats and the number you keep

• Three readings per session, for both length and girth - enough to see the spread without turning the session into an ordeal.
• Keep sessions short - state can drift if a session runs long, and drift breaks comparability between the three readings.
• Take the median of the three, not the mean, with this few readings - the median resists one outlier reading that the mean would not.
• If the spread across a session is wide, technique is the likely cause; if it is spread that only shows up across separate sessions, look at state instead - the two have different fixes.

Write the method next to the number

• Bone-pressed or not, dorsal or otherwise, state, instrument, date, time of day - a number without its method is not comparable to anything, including your own next reading.
• Record in centimetres to the nearest millimetre, and no finer than that - decimals beyond what the technique supports are not real precision.

What this card is not

It is not a substitute for reading the posts it links to the first time through - a line like "press firmly" means little without the explanation of what pressing loosely gets wrong. Treat it as a reference to check yourself against once you already understand each rule, the way a pilot's checklist assumes the training and only supplies the order.

It is also not a complete list of everything that can go wrong, only of what matters enough to be worth a line. Some genuine sources of error are small enough, or narrow enough in when they apply, that a card crowded with every last one of them would be harder to use than a shorter one that covers what actually moves a number by a millimetre or more in most sessions. If a reading still will not settle after checking every line here, the more exhaustive material this site carries on error and its sources is the next place to look, rather than assuming the card missed something.

It also is not a rubric for judging appearance, which is a different card entirely and lives elsewhere. Rate Cock works from a photograph rather than a tape and a ruler, and nothing on this card - state, landmark, tension, median - applies to how that works, because an image model is comparing pixels to other pixels rather than pressing anything to bone. The same separation holds for a numeric score or a person's verdict on the same kind of photograph: useful answers to a different question, with no card of their own that looks like this one, because nothing about them is a length in centimetres.