[Towertalk] Where to Place Guys for a Roof Tower?

[wd3q@erols.com (Eric Rosenberg)]

I'm about ready to put up a new (to me) roof tower, but have a question 
about guying (which the manual calls for).
It's one of those Japanese 3m (~10 ft) quadpod and a 4-sided straight 
section types (4.75 ft lower section, 6.5 ft upper section, with the 
sections bolted together). The the guy point is ~ 0.5m (20") down from 
the top. The rotor sits 1.5m
(~5 ft) below the top, with 3m (~10 ft) of the mast sticking out the 
top.

            ______
            |    |
            |    |
            |    |
            ------  << rotor goes ~ here (1.5m down from the top)
            |    |
            |    |
            |    |
            |    |
            ------
           /      \
          /        \
         /          \
         |<---1m---->|

My question is how do I determine where on my roof to put the 
guys...which is to say, what's the angle between the guys and the 
vertical section?

[The manual also shows the legs sitting against angle iron and *not* 
bolted down. This surprised me at first, but when I checked out the 
legs of the tower, I noticed that there were no bolt holes! As this is 
a replacement for another similarly base dimensioned (but smaller) roof 
tower, I'll be drilling holes to fit the existing feet.]

Thanks in advance,

Eric W3DQ
Washington, DC