Every manual I've seen has all kinds of specs for the "Vee" belts,
serpentine belts, and Gates belts.  Typically, they tell you to adjust the
idler to a certain deflection at so many pounds force at the center.
Tighter for new belts and looser for used.  Another method is with an
expensive special too.  A third method is to use a torque wrench on a
tensioning bracket.  This is often impossible with the engine in the car,
so I don't quite get the logic for a field manual.

Well, here's a better method and it works on all friction belts.  Start
tightening the belt while applying a rotational force to the driven pulley
by hand.  For instance, the alternator belt.  If you can turn the pulley by
hand easily (the crank being stationary), the belt is too loose.  Turn in
both directions and adjust for the maximum resistance.  If the pulley can
just be turned in the belt with maximum hand turning effort, the belt is
okay.

If you doubt this simple, foolproof method, then adjust to factory specs
and retest as described above and you will see they closely correlate.

There are also short cuts for bolts and nuts.  No need for torque wrenches.
Snug down your bolts, then give an extra 1/8 to 1/4 turn with a quick
"umph" on the wrench.  Do it in one quick motion rather than in steps,
because the friction will seize the bolt or nut in place before it is
driven home.  This is important: avoid torquing down with a ratchet wrench.
There is no feel in a ratchet.  Use a short box end wrench for final
tightening.  They are the correct length and couple closely for a good feel
for what the bolt or nut is doing.  Always grease your bolts and nuts with
anti-seize compound before you use this scientific method.  No, grease will
not cause your bolts to loosen; on the contrary, they will allow them to
stretch a little and lock the assembly together for a vibration resistant
attachment.