Wrong statement about unit default

[casella]

In http://beta.book.xogeny.com/behavior/equations/variables/, you state that the default for unit is "1". This is not true: the spec says the default is "", and rightly so, because saying dimensionless is different than saying unspecified dimension. If the default was "1", then this model would be wrong

Real m;
Force F;
Acceleration a;
equation
F = ma;

while it is actually ok, and the meaning of the default "" is that the compiler can actually infer that the unit of m is "kg". BTW, I would explain the meaning of unit="" explicitly in the text, and point out this difference.