The intellectual capital needed to calculate the means, moduli (scaling units) and quartiles in the last blog can be found in Airy, Theory of Errors of Observations (1875). The work appeared just before the start of Galton's series of publications on the normal distribution and heredity. Here is an index of the relevant sections.
§3 Law of probability, frequency of errors
mean error #24-6, p. 18f
squares of errors #27, p. 20
quartile #28-9, p. 22-3
§9, mean error, error of mean square #60-1, p. 45-8
§11, sum of weighted error #68, p.53
Airy's Theory of Errors also discusses solving for errors and "minimum squares" in §13, #87, p. 71f which are related to regression.