In a previous post Brian Whatcott says...

If a home-owner asks for advice, it is far, FAR better to err on the
conservative side, wouldn't you say? To put it another way:
whose advice would YOU take, if you were not in the field:
mine or Rob's?


Brian:

You can specify any product you want, including odd sized material. If
it suits your fancy call out 3-3/4" x 10-7/8" teak beam, but if you give
the homeowner advice about a product he cannot readily buy then you
begin to look foolish and the homeowner will begin to question whether
or not your advice was accurate.

Since "I" know this was not your intent, it is not really a problem for
me. But, if the person to whom you are giving advice is not an
engineer, then giving misleading or inadequate information can be a
problem. This is one of those issues where knowing the materials and
their specifications is important. It gives the homeowner a sense of
confidence that the engineer knows what he/she is talking about.

BTW, there are much better programs than "Archon" for computing stresses
in wood members. I'm partial to "Beamchek" which I use daily and is an
excellent tool for doing simple beam calculations in wood or steel. One
simply selects the material type (Douglas-Fir/Larch, Southern Pine,
steel, etc) and the software will input the appropriate "E" and "Fb"
values. Members will be then selected by the engineer from "standard"
manufactured sizes. This provides economical design. As in any good
software you can set your deflection limit to a more strict value than
the building code requires, thus giving you stiffer beams.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA