Serial Communication and Local Clock error calculation
Typically an asynchronous communication pin is sampled at 16 times the bit rate.  This implies a baudrate generator of:

\$\frac{24000000}{16}\frac{1}{38400} = 39.0625 \$

Since the resulting integer value is 39, the resulting error is:

\$\frac{0.0625}{39.0625} = 0.0016 \$

or 0.16%