Topic
Method
How to take a measurement that is repeatable and comparable.
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Volume from length and girth
Volume can be estimated from length and girth with a cylinder formula, but girth enters squared, so its small error becomes a large one in the result.
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NBPEL
Non-bone-pressed erect length: the ruler rests on the skin at the base, so whatever length is buried in the tissue in front of the bone goes uncounted.
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The fat pad, and the number it hides
The tissue in front of the pubic bone varies between people and within one person over time, which is the whole reason a bone-pressed reading exists.
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Erect or flaccid girth
Flaccid girth is even less stable than flaccid length; the literature's usable girth figures are erect, and that is the one to record.
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False precision
A converted figure with two decimals carries the precision of the original, not of the decimals; quoting it finer than it was measured is a small dishonesty.
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Finding the landmark
Bone-pressed means the ruler stops on bone at the base, above the shaft; here is how to find that spot and know you have it.
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Precise, accurate, or neither
Three tight readings can all be wrong the same way, and three scattered readings can average to the truth; the two problems have different fixes.
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How hard to press
Bone-pressed is a stop, not a force; the reading is repeatable when the ruler stops on bone every time, and it wanders when pressure varies.
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The measurement card
Every rule that matters, on one card: state, landmark, line, angle, site, tension, three readings, median, method line.
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Hair in the way
Hair at the base can stop the ruler short of the bone by a few millimetres and does so inconsistently; part it or trim it before measuring.
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When only a tape is to hand
A flexible tape used for length follows the shaft's contour and bends into the fat pad, and both effects add length; if you must, here is how to limit them.
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What to write down
A reading without its conditions is not data; the log needs date, state, method, site, instrument and all three raw readings, not just the answer.
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What to round to
Report to the resolution your instrument and technique can support - a millimetre or an eighth of an inch - and never finer than the spread of your readings.
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How many readings
Three readings in one session, and three sessions on separate days, is the practical minimum that lets you see the spread and take a central value.
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Marks from the first reading
A tape or ruler pressed hard leaves a temporary indentation, and a second reading taken on it lands low; wait a moment or move the site.
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Keep the tape square to the shaft
A tape wrapped at an angle traces an ellipse rather than a circle and always reads high; perpendicular to the axis is the specification.
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The first reading
The first careful reading most people take is the highest they will get, because everything from pressure to angle is unconsciously chosen and later readings regress.
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Which way the ruler points
A ruler held level while the shaft points upward reads a projection, and a ruler tilted past the shaft reads long; the rule is parallel to the shaft axis.
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Systematic and random error
Random error averages out with repeats; systematic error does not, and most self-measurement error is systematic and points the same way.
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How far to stretch
Stretched length is taken at the point where the tissue resists further extension, and inconsistent tension is the main reason the number moves.
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Session length
A session should be short enough that erection state stays constant across the three readings; if it takes long enough to change, the readings are not comparable.
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Centimetres and scores are different objects
A length is a distance with an uncertainty; a rating is a judgement with a rubric. Confusing them is how a ruler ends up arguing with a score.
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Rounding bias
Most people round toward the next half-centimetre or half-inch when the reading is between marks; writing the raw mark before deciding is the fix.
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How the tip meets the ruler
The reading is where the tip reaches on a ruler laid alongside; pushing the ruler into the glans, or holding it off the tip, shifts the mark by millimetres.
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Where the measurement ends
Length ends at the tip of the glans in a straight line from the base - not at the meatus, and not at the far point of a curve.
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Inside a study measurement
A participant in a clinical size study is measured standing, by a trained observer, with a rigid ruler and a tape, in a room kept warm, under a written protocol.
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Measuring curvature
Curvature is reported as an angle between the base axis and the distal axis; here is how it is measured and why it shortens the straight-line length reading.
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The ventral line
The underside runs from the scrotal junction and follows any upward curve, so it is longer than the dorsal line by an amount that varies with anatomy.
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How tight the tape should be
Snug means the tape touches skin all the way round without indenting it; tighter compresses tissue and reads low, looser reads high.
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Why flaccid readings wander
Flaccid length responds to temperature, arousal, time of day and recent activity, which is why the literature reports it with wide spread and few people should bother taking it.
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Bone-pressed or not: the two length numbers
Two legitimate length measurements exist, they differ by a variable amount, and only one of them is comparable to the published data.
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Standing or supine
Studies mostly measure standing; lying down changes the fat pad, the shaft angle and your view of the ruler, so posture belongs in the method line.
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Reading blind
Mark the tip position with a finger or clip, take the ruler away, then read it; separating the act of measuring from the act of reading removes expectation.
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Why length is taken along the top
Dorsal, lateral and ventral lines give three different lengths on the same shaft; the literature uses the top, and this is why.
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Held horizontal, or left alone
Pressing an upward-pointing shaft down to horizontal for the ruler changes the reading; measure along the axis at its natural angle and say so.
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Why centimetres
The literature reports in centimetres, a millimetre is a cleaner resolution than a sixteenth, and one conversion at the end beats one at every step.
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Mean or median
With three or five readings the median resists one bad reading; with many readings the mean uses more of the information. Use the median for small sets.
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How the erect figures were taken
Erect measurements in the literature come from pharmacologically induced erections, self-stimulation in private, or self-report of an at-home reading; each is a different dataset.
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Finding midshaft
Midshaft girth is taken halfway between the base and the corona; here is how to find that point and keep it the same next time.
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You and the clinician read differently
A clinician and a self-measurer using the same ruler still diverge, for reasons of angle, motive and landmark rather than honesty.
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The other hand
Gripping the shaft to steady it while you wrap compresses tissue near the grip and can move the girth reading; hold at the base, away from the tape.
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Temperature and the reading
Cold shortens a flaccid reading noticeably and warmth lengthens it; erect readings are far less sensitive, which is one more reason to report erect.
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The method line
A single line - BP, erect, dorsal, rigid ruler, median of three - makes a figure comparable; without it the number is an anecdote.
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A second pair of hands
A partner reading the ruler removes your viewing-angle problem and adds an inter-observer one; here is how to brief them so the swap is a gain.
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Reading a plus-minus
A ยฑ is a statement about your readings, not a guarantee about the true value; it says the next careful reading will most likely fall inside.
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Why girth is not one number
The shaft tapers, thickens or bulges differently from person to person, so a girth reading is only meaningful with the site attached.
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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.
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Looking down at the ruler
Reading a ruler from above and behind foreshortens the scale and shifts the tip mark; sighting square to the ruler removes a small but consistent bias.
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Bone-pressed length, start to finish
The definitive walkthrough of the length measurement the literature reports - landmark, pressure, line, tip, reading, repeats and how to write it down.
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Where the error comes from
Two readings of the same person twenty minutes apart can differ by more than a centimetre. Almost none of that is the ruler.
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Stretched flaccid length, and why the clinics take it
What stretched length is, why the literature leans on it, how it is taken to a resistance point, and how it sits against an erect reading.
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Girth, done the way the studies do it
Everything that decides a girth reading in one place - where on the shaft, how snug, tape perpendicular, what state, how to read and repeat.
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The measurement glossary
BPEL, NBPEL, stretched, midshaft girth, precision, systematic error, nomogram - each term in one or two sentences with a pointer to the post that explains it.
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How to measure the way the research does
Most of the disagreement online is people comparing numbers taken by different methods. There is only one that is comparable, and it takes two minutes.