[9*(sigma from 1 to inf) 10^-x converges to 1]. This may seem like an approx, but it is not. When an infinite series converges to a number, it IS that exact number. This concept is used in calculus all the time for finding area under curves. By saying that 0.999~ is not = 1, you are basically saying that integral calculus is useless (because integration is based on summing up an inf number of rectangles, kind of like the inf series shown above).