The advance test unit is always prudent, but I can't see why it should be
dug in arbitrary levels.
 
Any test should be dug by "natural" levels, if they can be recognized.
There is something to be said for limiting levels, in the initial tests, to
some arbitrary quantity, such as ten centimeters.
 
After all, it can be said that every excavation unit is a test!
 
 
    _____
___(_____)
|"Baby"  \
|1969 Land\_===__    See Baby performing at Assateague during
|IIA__Rover   ___|o  the R.O.V.E.R.S. RTV driving test event!
|_/ . \______/ . ||  http://www.aircast.com/peterg/assat7.JPG
___\_/________\_/____________________________________________
Ned Heite, Camden, DE  http://home.dmv.com/~eheite/index.html