Trace math is a powerful tool for comparing two traces to each other by using mathematical operations. To perform trace math, select the trace menu (by pressing the Shift key and the Trace (5) key), and then select the active trace. Press the Save Trace to Memory soft key to save a copy of the trace into the instrument memory. When trace TR1 is saved to memory, an M1 memory trace is produced. Each trace can have one associated memory trace.

You can display Trace Only, Memory Only, or Trace and Memory. Press the Display soft key in the Trace menu to open the Display menu. Then press the desired soft key to select trace or trace memory, or both. To make distinguishing traces easier, the memory trace is assigned a different color than the original trace. The corresponding memory trace number (shown in the Instrument Settings Summary) uses a matching color. When viewing Memory Only, the Instrument Settings Summary displays the information for M1. When viewing Trace and Memory, the M1 information is displayed above the TR1 information.

At this point, the trace has been saved only to memory, and no trace math has been applied to it. Click on the Trace Math soft key to apply one of the following functions: subtraction, addition, multiplication, or division. The mathematical function operates on the complex numbers for each of the traces. When dividing TR1 by M1, the result is the point‑by‑point division of the complex numbers for each trace. Note that when trace math is applied to a trace, the function is displayed in the instrument status window. In the above example, assuming that S11 is the S‑parameter that is associated with TR1, the status would display TR1: S11/M1.

If a trace is saved to memory, and if some settings on the trace are then changed (such as S-parameters, frequency, or number of points), then a mismatch occurs between the trace and memory. The vector network analyzer allows you to change these trace settings, but it places an asterisk next to the memory trace name in the instrument status window to point out the mismatch. In the previous example, if a setting is changed on TR1 (relative to the memory trace M1), then the listed filename is displayed as: M1: S11*. A similar mismatch occurs if you save a measurement when trace math is applied (TR1: S11/M1, for example). When that measurement is recalled, the result of the trace math is still stored in the memory location. The trace math function, however, is no longer valid, and the memory trace contains only the resulting S‑parameter (S11 in this example). To indicate that the data that are stored in the memory location is based on previous measurements and calculations, the ^ sign is placed next to the memory name: M1: S11^.