The last(1) command reads wtmp. If you want super-details, you can get the source code for last(1) and examine the format details. If you want to read wtmp in a standard way, just use <B>last</B>.
Also, you can do a man on both <B>last</B> and <B>wmtp</B> to get high level, general details.
[Edited by Neo on 12-13-2000 at 02:33 AM]