It is a book referring to Spain in the late 16th century!
Spanish ducats, each one roughly equivalent in the later sixteenth century to one escudo, or crown and to two florins. About four ducats made up one pound sterling.
I found that quite a few coins were sharing the same name in the era! What are actually these coins, like the so-called Spanish ducat?
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The biography written by Geoffrey Parker is about Philip II! (Imprudent King ?? ). G. Parker said that all moneys mentioned were calculated in Spanish ducat to get rid of confusion, then came what I have quoted.