[ATM] Calculating Focuser Length and Travel

[alaudet at timminsastronomy.com (Al Audet)]

Hello group.
I have been lurking for a few weeks and must say I am amazed at the 
discussion around here.  Excellent stuff.

I have undertaken my first scope, an 8" f/6 (classic Dob Sidewalk 
Telescope).
I have a question about calculating focuser length and travel.  I have 
read instructions and combed archives, but being a very visual person I 
can't make sense of weather or not the focuser should be racked all the 
way in parallel to where the tube hole starts, which gives me a focuser 
length of 4.25".

See image1 (focuser racked in)
See image2 (focuser racked in measures 4.25")

If I then rack it "out" all the way then it is about 5".

See image3 (focuser extended all the way out to 5")

Therefore do I have a focuser of 4.25" with .75" of travel? Is this correct?

I then interpreted another article saying that I should extend it about 
half way and that is my focuser length (4.625 with .75" of travel), 
travel being the length it has left to go in either direction.

Image1, 2 and 3 can be seen here

http://www.timminsastronomy.com/pics/atm/

I apologize if this is a FAQ but I did spend time googling the net and 
looking at the archives and was not able to find anything that I could 
be 100% sure of.

Best regards and thanks for any clarification you can provide.

Al Audet