Because we use base 10, not base 2, floating point numbers have a non-integral number of digits of precision. When showing them as strings, the next lower number of digits of precision is used, and what you see is slightly rounded. So $period and $in_view can be not quite equal and still stringify to the same thing.

This is generally regarded as a good thing, since people don't expect print .1 to produce "0.10000000000000001" instead of ".1".