Hutchins has his own way of looking at the world.
To my my taste, a more accurate statment would be analog-to-fractional-to-digital. The chip log divides the hour fractionally into units of speed. A 32-point compass (which was the norm for most of the history of Western seafaring) divides the compass rose fractionally based on four cardinal points.
Today we accept mathematics as the language of understanding the world. But mariners of yesteryear were mostly simple men, and tended to think fractionally, i.e. in terms of ratios. Not an exclusive thing. They certainly used mathematics, too. But the ratio of one thing to another was the fundamental Greek way of interpreting the sciences, and the Greeks held sway over the sciences even after the Arabs invented the decimal point. We eventually got to a digital (mathematical) way of looking at the world, but we had a geometrical (ratio-based, or fractional) way of looking at it for far longer.
To my taste Hutchins overstates his thesis. He claims, “The navigation chart is an analog computer. Clearly, all problems that are solved on charts could be represented as equations and solved by symbol processing techniques.” Which is true. But you could also say that the English language is a code, and the code can be rendered into binary code and read using digital technology. That statement is true also, but It is a very narrow specialist view of the English language. It tells you nothing about the roots of the English language, or how it developed, or the reason why it persists. Not to say anything bad about Hutchins. He’s not talking about history I guess.
To my mind, charts were invented as a roughly proportional representation of geography, which after many centuries were crafted to be analyzed using exact geometric and fractional methods. Which is what Hutchins means as a chart being an analog computer. But the sticking point for me comes down to the single word “digital”.
In Figure 1.2 before Hutchins shows the view through an alidade, showing how information is transposed from analog to digital. But if you had used a similar instrument in 1821 it is likely the bearing would have been in points rather than degrees. Navigation had not advanced sufficently for degrees to be universally used to divide a circle. Are points --a fraction of a 32-point compass system–digital information? A matter of semantics, I suppose.