Peterson iStroboSoft - Manual (Page 4)

The Drop/Capo menu item provides a simple means of transposing note names for
instruments built around something other than Concert C pitch (for example, a B for
clarinet or E for saxophone).
For example, when a guitar is in its standard tuning, we commonly call the open
string notes: E, A, D, G, B, and E. These are the Concert C key signature note names
for those sound frequencies. However, guitarists commonly think of this tuning as
standard E tuning because of the preponderance of Key of E notes.
Obviously, this can get confusing.
The Drop/Capo function provides an optional numbering system for key transposition
which corresponds to the equivalent fret “stop” of the strings.
For example, if you apply a capo (on a standard-tuned guitar) on the 3rd fret, the
new “open string” notes without key transposition would be: G, C, F, A#, D, and G.
If you would like to tune these new “open string” notes without having to mentally
transpose note names, you would simply select a Drop/Capo key value of “+3” which
corresponds to the 3rd fret in this example. In this case, the “open string” notes will
once again be displayed as E, A,D, G, B, and E on the screen.
To carry the analogy further, the open strings without a capo (the normal case of the
nut stopping the strings) is equivalent to the 0th fret and so yields the standard note
names for the open strings. Further, if you detune the strings down as in "half-step
drop” (or “flat”) tuning, this would be equivalent to having an "extra fret” as the stop
in the opposite direction. Hence, the Drop/Capo value to use would be “-1”.
For advanced users employing non-equal temperaments, key transposition still
affects only the note names for use with non-Concert C instruments. The tonic or
root frequency of the temperament remains at Concert C pitch.
Default setting is: +0 [Key: C]
Calibration
Calibrating iStroboSoft™
iStroboSoft will measure and display to within 0.1 cent accuracy throughout its full
range. However, there may be instances when measurements do not match when
compared to an external tuner. In such a case, the external tuner may be
inaccurate, or iStroboSoft may be subject to biasing introduced by an inaccurate
reference clock in its host device.
This inaccurate reference clock inserts a 'bias' onto the audio signal during
processing. This bias can be enough to sway an otherwise accurate measurement by
as much as +/- 3 cents!
To allow these host devices to be used to accurately tune instruments, iStroboSoft
has a calibration feature which will independently allow it to calibrate to an external
audio source and measure the offset of the bias to ensure an optimal measurement.
This calibration is remembered permanently until you remove it.