Pytheas took the altitude of the Sun at Massalia at noon on the longest day of the year and found that the tangent was the proportion of 120 (the length of the gnōmōn) to 1/5 less than 42 (the length of the shadow). Hipparchus, relying on the authority of Pytheas (says Strabo), states that the ratio is the same as for Byzantium and that the two therefore are on the same parallel. Nansen and others prefer to give the cotangent 209/600, which is the inverse of the tangent, but the angle is greater than 45° and it is the tangent that Strabo states. His number system did not permit him to express it as a decimal but the tangent is about 2.87.