On Tuesday, 21 June 2011 20:18:16 UTC+10, Helmut Wabnig wrote:

What I learned is, a metallic boom requires a small +length correction
of the dipole elements. YAGICAD does it automatically with a cryptic
value called L+BCF (boom correction factor?)

If you Google for "boom correction factor", you should find a wealth of discussion on the subject. It is not all cut and dried, it remains an area of active research.

Owen