This note explores an often overlooked question about the characterization of the notion model of computation which was originally identified by Cobham. A simple formulation is as follows: what primitive operations are allowable in the definition of a model such that its time and space complexity measures provide accurate gauges of practical computational difficulty? After exploring the significance of this question in the context of subsequent work on machine models and simulations, an adaptation of Kreisel's squeezing argument for Church's Thesis involving Gandy machines is sketched which potentially bears on this question.
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