This article is from the ZTerm FAQ, by Les Jones firstname.lastname@example.org with numerous contributions by others.
It may not be low at all. Ignore the percent efficiency figure. The
characters per second (cps) rate is a better indicator of
The reason you should ignore the percent efficiency is that ZTerm
normally calculates percent transfer efficiency by dividing the
actual throughput by the DTE speed (what ZTerm calls the data
rate). Assuming your modem is transferring data at exactly 14400,
ZTerm will report the efficiency to be 14400/19200 = 75% at 19200,
14400/38400 = 38% at 38400, and 14400/57600 = 25% at 57600. Yet in
each case the actual transfer rate is the same.
Having said all of that, you can use the percent efficiency figure
if you initialize your modem with ATW2. When the modem is set to
W2, ZTerm reports the connect speed as the DCE speed rather than
the DTE speed, and calculates percent efficiency based on the DCE
speed. So if your modem is transferring data at exactly 14400,
ZTerm will report the efficiency to be 14400/14400 = 100%.