I thought I should introduce myself. I'm a newbie in letterpress and currently restoring (or at least trying to restore) a Poco#0 press.
For the longest time I could not understand how the tympan/frisket thing works on a Poco (ps. I kept looking at Neil Giroux's photos without understanding it). Until I saw Preston's website with an explanation.
Also, there is book called "Printing on the Iron Handpress" by Rummonds that explains how the tympan/frisket works in the traditional iron handpress. Great book, worth every penny.
Anyways, I look forward to learning more about the Poco.