While sound in theory, in practice Aristarchus's procedure is highly inaccurate in the Earth/Sun/Moon case; this is because EM is much smaller than ES, implying that b is very close to 90 degrees, so that c is in turn very small. This has the consequence that a small measurement error on translates in a large variation in the ratio EM/ES (again in modern parlance, a measurement error db is amplified by a factor 1/(sinc)^2, which is large when c is very small). Aristarchus mesured b=87 degrees, while the true value is in fact 89 degrees 50 minutes. This may seem a small error, but because of the large error amplification Aristarchus' value leads to EM/ES=19, instead of the true value EM/ES=397. Nonetheless, Aristarchus' calculation was the first to mathematically set the spatial scale of the cosmos.