1. While most pages call the bit 6 and 7 of $4000/4004 as duty, the length counter page calls them sequence.
2. I followed the APU Sweep page and completely missed the point that
A NES APU sweep unit can be made to periodically adjust a pulse channel's period up or down.
means the reload flag will be set periodically. I suggest mentioning this fact in the main text below.
3. Add frame counter to the flow charts. Having 1 starting point in a flow chart makes it easier to follow.