Configure Measurements (Top-Base Definition tab)

Click Measure > Configure Base Measurements to open this dialog.

Use the Top-Base Definition tab of the Configure Measurements dialog box to define the top and base levels which are used to locate the lower, middle, and upper threshold levels.

• How top and base values are used to identify waveforms

You can select either Auto or Custom Top-Base Definitions.

Measurements Affected by Top-Base Definitions

Instrument Mode
Oscilloscope	Eye	TDR/TDT
Average	Eye Amplitude	Average
Duty Cycle	Eye Height	Fall Time
Fall Time	Eye Width	Rise Time
Rise Time	One Level	Δ Time
Frequency	Zero Level	Time at Edge
Preshoot	Fall Time	Time at Amplitude
Oversoot	Rise Time
Period	Crossing Time
+ Pulse Width	Δ Time
— Pulse Width	Crossing %
Δ Time	Duty Cycle Distortion
Time at Edge	Signal to Noise Ratio
Time at Amplitude	Jitter
RMS	Extinction Ratio
Amplitude at Upper	OMA at Crossing
Amplitude at Middle	VECP
Amplitude at Lower	Bit Rate
OMA	VECP
Phase
Jitter

Auto Top-Base Definitions

The Auto (default) setting computes the top (100%) and base (0%) levels, which are relative or proportional to the signal amplitude.

Custom Top-Base Definitions

The Custom setting allows you to enter absolute values for the top-base levels. Setting custom thresholds causes the measurement results table to display the text "user defined." The following table shows the amplitude units for the various waveform content windows.

Units Used for Displayed Content Window Graphs

Name of Content Window Graphs	Amplitude Units	Example Source Waveform Selections
Oscilloscope, Eye, and TDR/TDT Modes
Window	Volts and Watts	Channel 2B Differential 1A Port 1+ (1A)
TDR/TDT T-Domain Parameters
Time-Ohms	Ohms	T11 Ohms
Time-Volts	Volts	TCC21 Volts
Time-%	Percent	T21 Percent
TDR/TDT S-Parameters and FFT Math Operator Waveforms
Freq-Mag	Decibels	FFT[2A] (F1) S21 Magnitude
Phase	Degrees	FFT[2A] (F2) S12 Phase
GrpDelay	Seconds	FFT[2A] (F3) SCD11 Delay