Just a reminder, a scientific instrument is something that is primarily meant to be used to conduct science.

Just because something can be used for doing science or because science was used/necessary in creating it, does not make it a scientific instrument.

Otherwise we had to conclude that pretty much every manmade object in existence is a science instrument. (Dare me, show me an object and I can tell you how you can do science with it or how science was needed to create the object)

And calculating the date of Easter has absolutely nothing to do with science.

I know many people see couple of numbers and conclude science was being done, but that is not true. Science is about improving our understanding of the universe. Doing "sciency" stuff like observing the sky or calculating formulas or measuring time for some other reason IS NOT science.