Suppose the actual length of a person’s index finger is 80.5 mm and the actual length of his/her ring finger is 83.5 mm. Then the 2D:4D ratio is 0.964. A measurement error of 0.5 mm is very easy to make, e.g. due to inaccuracy of a photocopier, inaccuracy of a ruler, inexactness of where a finger joins the hand (and even if it wasn’t a vague concept it would still be a problem to pinpoint the precise location of it with a great accuracy) and even differences in muscle tension in fingers at the particular moment of placing a hand in a photocopier. If a person measures his/her index finger as being 80 mm long (0.5 mm shorter) and her/his ring finger as being 84 mm long (0.5 mm longer), then they would obtain 2D:4D ratio of 0.952. Whereas if the length of the index finger is measured to be 81 mm, and the length of the ring finger is 83 mm, then 2D:4D ratio is 0.976. Therefore, the first digit after the decimal point does not vary that much (in the vast majority of all cases it is 9), the third one is basically noise, and even the second one is not that reliable (in an individual case). However, that might still be enough to notice some interesting correlations and if the errors are symmetric it might not even matter that much when all data will be aggregated.
Suppose the actual length of a person’s index finger is 80.5 mm and the actual length of his/her ring finger is 83.5 mm. Then the 2D:4D ratio is 0.964. A measurement error of 0.5 mm is very easy to make, e.g. due to inaccuracy of a photocopier, inaccuracy of a ruler, inexactness of where a finger joins the hand (and even if it wasn’t a vague concept it would still be a problem to pinpoint the precise location of it with a great accuracy) and even differences in muscle tension in fingers at the particular moment of placing a hand in a photocopier. If a person measures his/her index finger as being 80 mm long (0.5 mm shorter) and her/his ring finger as being 84 mm long (0.5 mm longer), then they would obtain 2D:4D ratio of 0.952. Whereas if the length of the index finger is measured to be 81 mm, and the length of the ring finger is 83 mm, then 2D:4D ratio is 0.976. Therefore, the first digit after the decimal point does not vary that much (in the vast majority of all cases it is 9), the third one is basically noise, and even the second one is not that reliable (in an individual case). However, that might still be enough to notice some interesting correlations and if the errors are symmetric it might not even matter that much when all data will be aggregated.