Survey: Errors up to ¾" (20 mm) common in penis length measurements
There are two ways to measure the length of an erect penis.
1. Place a ruler at the base of your penis where it meets the pelvic bone. Make sure the ruler is just touching the skin at the pelvic bone. DO NOT PUSH IT INWARD. Now measure from this point to the very tip of your penis.
2. The same, but this time You DO PUSH IT INWARD. Using this method the soft tissue (mainly fat) between ruler and the pelvic bone is compressed and the result of the measurement gives a little longer result.
The first method is common in studies accomplished by scientists and medical researches.
The second method is more likely to be used in Self-reported-Internet surveys.
In an Internet-survey accomplished in Finnish website in Finland, visitors in the penis size statistics website were asked to measure their erect penis length using both methods.
Results: an average difference between both measuring methods was 10.4 mm (0.416 inch), but the distribution over the whole scale from 0 to 20 mm was evenly distributed.
The results suggest that penis length statistics are not very precise and measurement errors are common ranging evenly from 0 - 20 mm or 0" to over ¾".
The Finnish web-site containing the differences-in-measurement-poll was same kind of Penis-size comparison with java-robots as this site in English:
Penis-size java comparators
The original Java Comparison Site in Finnish