EXFO FTB-500 (Window XP) - Manual (Page 189)

Preparing for Automation
FTB-500 179
Getting Optimum Performance from Your FTB-500
Getting Optimum Performance from Your
FTB-500
Several factors influence the data transfer rate of an FTB-500. The
information presented hereafter will help you get the best transfer rate
possible.

Output unit (RS-232, ActiveX and TCP/IP): The FTB-500 can return
results in

linear units (for example, watts)

log units (for example, dBm)
Since internal units are linear, you will get optimal performance by
using linear units for output (no need for an internal conversion to log).
Note: You must make the choice of output unit for each instrument offering such
a feature. Refer to the user guide of each optical instrument for a list of
available commands and queries.