yes that's the one. I didn't read or understand all of it, but it helped me a lot realize what i considered as weird (the dx object and the whole notation around derivative) was not due to comprehension problems on my part, but due to the fact that the field was still a work in progress.
Unfortunately, that realization came 25 years too late.
Was this book "Elementary Calculus: An Infinitesimal Approach", by Keisler? It's an awesome book. It's free to download at https://people.math.wisc.edu/~hkeisler/calc.html