Lorn (and anyone else who doesn't have one) --

The small digital levels cost about $80, or they did a few years ago when I
bought mine.  It's about 8 inches long, but can be quickly inserted and clamped
into a "holder bar" that is about two feet long.  They probably even make
longer holder bars.

This tool is indispensable for precisely (har, har) doing what you were
describing.  It is also incredibly useful for measuring control surface travel,
setting control stops, and other such things.  One thing is is NOT good for is
precise leveling of your airplane prior to bonding on tails, setting wing
incidence, and other precision measurements of flying surfaces.  For those tasks, I
would stick with the water levels, transits, plumb bobs, and the like.

As a hint, next time you have your plane EXACTLY LEVEL (using the plumb bobs
and all that crap), take the digital level and find a "sweet spot" on the
canopy rails.  This will be a spot where the digital level reads zero -- parallel
to the ground.  You will be surprised to discover that there may only be one
spot where this is true.  The other spots will be off by some tiny fraction of
a degree.

There are plenty of times where absolute precision is not required, but you
want to get pretty darn close.  I use those "sweet spots" on the canopy rail
and seat back rail to level my airplane for certain tasks.  An example is
footwell floors -- they don't have to be perfectly level left-to-right like a
horizontal tail does, but you don't want it obviously tilted.  Consoles may be
another such place.  Instrument panel mounting.  Seat back closeouts, if you're
putting your battery there, are another example.  You can level your plane pretty
darn close this way but not close enough for mounting flying surfaces.

Make sure you run through the calibration process (and put the instructions
in your toolbox because you cannot remember them) when you get the tool and if
you drop it.  And maybe every Christmas.  It's pretty easy and only takes five
minutes.

- Rob Wolf
LNC2 70%