  This paper is concerned with the numerical implementation of a formula in the
enclosure method as applied to a prototype inverse initial boundary value
problem for thermal imaging in a one-space dimension. A precise error estimate
of the formula is given and the effect on the discretization of the used
integral of the measured data in the formula is studied. The formula requires a
large frequency to converge; however, the number of time interval divisions
grows exponetially as the frequency increases. Therefore, for a given number of
divisions, we fixed the trusted frequency region of convergence with some given
error bound. The trusted frequency region is computed theoretically using
theorems provided in this paper and is numerically implemented for various
cases.
