Fluke 91 Series II User Manual page 54

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RPM 1 METER (revolutions per minute) Measure one
count per revolution in Meter mode.
RPM 2 METER (revolutions per minute) Measure one
count per two revolutions in Meter mode.
dt (delta time) SCOPE Measure the time difference
between the (vertical) cursors in Scope mode.
1/dt (frequency) SCOPE Measure
frequency of the waveform in Scope mode. It is shown as
the reciprocal value of the time difference (dt) between the
vertical cursors.
rise time SCOPE Measure the rise time between 10%
and 90% points of the first rising slope of the waveform in
Scope mode. First use
0% and 100% points of the waveform. These are the
intersection of the cursors with the waveform. Set the rising
slope to at least four time divisions for a precise
measurement. The rise time is now instantly displayed.
the relative
and to determine the
91/92/96/99/105
Figure 3-3 Rise Time Measurement
Users Manual