 At the time Turing was writing his paper, the modern computer was not developed yet and so rephrasings of Turing’s thesis which identify Turing computability with computability by a modern computer are interpretations rather than historically correct statements of Turing’s thesis. The existing computing machines at the time Turing wrote his paper, such as the differential analyzer or desk calculators, were quite restricted in what they could compute and were used in a context of human computational practices (Grier 2007). It is thus not surprising that Turing did not attempt to formalize machine computation but rather human computation and so computable problems in Turing’s paper become computable by human means. This is very explicit in Section 9 of Turing 1936–7 where he shows that Turing machines are a ‘natural’ model of (human) computation by analyzing the process of human computation. The analysis results in a kind of abstract human ‘computor’ who fulfills a set of different conditions that are rooted in Turing’s recognition of a set of human limitations which restrict what we can compute (of our sensory apparatus but also of our mental apparatus). This ‘computor’ computes (real) numbers on an infinite one-dimensional tape divided into squares [Note: Turing assumed that the reduction of the 2-dimensional character of the paper a human mathematician usually works on “is not essential of computation” (Turing 1936–7: 249)]. It has the following restrictions (Gandy 1988; Sieg 1994):