Why did Giovanni Fontana write his book in cipher?

[Mark Knowles]

Some might argue that the Voynich manuscript was a highly technical work.

No they wouldn't. The Voynich shows no attempt at perspective, at physics, at mechanism, at automatism. It is purely based in allegory of earlier centuries.

Given that we don't know what it says how can we say that it wasn't high technical? I suppose it depends on what one means by "technical". Clearly the Voynich has different content from Fontana's work, but one could see that as the difference between a book about engineering compared to a book about biology.