> How different is my Calculus 1 textbook Ed. 17 from this year's Ed. 18?
There's almost certainly no significant mathematical difference as far as the calculus it teaches goes.
If the target audience for the book includes students who aren't really interested in calculus, such as students who are just taking it to fulfill a requirement, and don't expect to use calculus much after they finish the class, then I'd expect the new edition to update exercises and examples to try to make them interesting and relevant to today's youth.
If the target audience is students who actually want to learn calculus, either because it is interesting to them per se, or because they know it is useful for things that do interest them, then there is probably little or no need for frequent new editions.
For example, a few top schools use Apostol's two volume text, "Calculus", either as their main calculus text, or for the more advanced track if they have multiple calculus tracks. Apostol volume 1 is currently all the way up to 2nd edition, which came out in 1967. Volume 2 is also on its 2nd edition, which came out in 1969.
Another example is Spivak's "Calculus", also used at several top schools, which is on its 4th edition, which came out in 2008. According to the preface, "Although small changes have been made to some material, especially in Chapter 5 and 20, this edition differs mainly in the introduction of additional problems, a complete update of the Suggested Reading, and the correction of numerous errors". The preface to the 3rd edition says that the biggest change was the addition of a chapter on planetary motion. It also rearranged quite a bit of material, and added problems. It looks like 2nd edition was a pretty substantial upgrade over 1st edition.
Spivak 1st edition was 1967, 2nd edition 1980, 3rd 1994, and 4th 2008.
There's almost certainly no significant mathematical difference as far as the calculus it teaches goes.
If the target audience for the book includes students who aren't really interested in calculus, such as students who are just taking it to fulfill a requirement, and don't expect to use calculus much after they finish the class, then I'd expect the new edition to update exercises and examples to try to make them interesting and relevant to today's youth.
If the target audience is students who actually want to learn calculus, either because it is interesting to them per se, or because they know it is useful for things that do interest them, then there is probably little or no need for frequent new editions.
For example, a few top schools use Apostol's two volume text, "Calculus", either as their main calculus text, or for the more advanced track if they have multiple calculus tracks. Apostol volume 1 is currently all the way up to 2nd edition, which came out in 1967. Volume 2 is also on its 2nd edition, which came out in 1969.
Another example is Spivak's "Calculus", also used at several top schools, which is on its 4th edition, which came out in 2008. According to the preface, "Although small changes have been made to some material, especially in Chapter 5 and 20, this edition differs mainly in the introduction of additional problems, a complete update of the Suggested Reading, and the correction of numerous errors". The preface to the 3rd edition says that the biggest change was the addition of a chapter on planetary motion. It also rearranged quite a bit of material, and added problems. It looks like 2nd edition was a pretty substantial upgrade over 1st edition.
Spivak 1st edition was 1967, 2nd edition 1980, 3rd 1994, and 4th 2008.