I have been doing some research on clock escapements.  Turns out 
pendulum escapements aren't period by about 65 years.  Verge and foliot 
with a crown wheel where the pallets engage with opposite sides of the 
crown wheel are.  There are some verge and foiliot escapement designs 
which have 2 gears with pins that replace the crown wheel and the 
pallets both engage the top of these two pin gears.  I am looking to 
prove or disprove weather this type is also period.  Any help would be 
appreciated.  A simple search on firefox gives a great overview on 
wickipedia, and www.youtube.com/watch?v=7HgAtCn3VUU shows the two 
pin-wheeled type.?