Ion 1.1 Timestamp Scale/Mantissa

[almann]

What is interesting, is what we're calling an implicitly negative exponent, is what other people would call scale and not only that, but our restrictions on the coefficient/scale are what, in other contexts, would be called a mantissa. I am not sure that we need to introduce mantissa (fractional seconds is probably good enough), but we might consider calling this negative exponent scale.

Originally posted by @almann in https://github.com/amazon-ion/ion-docs/pull/215#discussion_r1196850547