_S_ for _CT_ 5.0 must be considered correct, or the principle of the
error curve will not apply.

The method of computation may be derived in the following way: If we
take the origin so that the maximum of the error curve falls on the
_Y_ axis, the equation of the curve becomes

y = ke^{-[gamma]²x²}

and, assuming two points (x_{1} y_{1}) and (x_{2} y_{2}) on the
curve, we deduce the formula

____________
±D \/ log k/y_{1}
x_{1} = ---------------------------------
____________ ____________
\/ log k/y_{1} ± \/ log k/y_{2}


where D = x_{1} ± x_{2}, and k = value of y when x = 0.

x_{1} and x_{2} must, however, not be great, since the condition
that the curve with which we are dealing shall approximate the form
denoted by the equation is more nearly fulfilled by those portions of
the curve lying nearest to the _Y_ axis.

Now since for any ordinates, y_{1} and y_{2} which we may select
from the table, we know the value of x_{1} ± x_{2}, we can compute
the value of x_{1}, which conversely gives us the amount to be added
to or subtracted from a given term in the series of _CT_'s to produce