The boundary conditions given by Z.P. Liao et al. (Scientia Sinica, vol. XXVII, no. 10, p. 1065, Oct. 1984) have been shown to yield excellent results in scalar as well as vector electromagnetics problems using double-precision arithmetic. However, it is more desirable to use single-precision arithmetic if possible, since the time required to perform a real, double-precision multiplication is two to three times that of a single-precision operation. But with a single-precision implementation, it is observed that the solution becomes unstable as the number of time steps grows. The authors present a procedure for remedying this problem.