```in - integrate a part of stack 1

EXAMPLES:
in 40,60		Integrate from 40 to 60 Km/s (if horiz plot units are
Km/s). Print the results and put in area1.

cr 2;in,x(0),x(1)	Read the cursor twice and integrate between those limits.
This is the macro "crin"

in !0 !1 dp:;v ?(.area arg3 * the error in the area and
otherwise gives DRAGON (aka IEEE NaN, aka BLANK).

in clip:1,1		Use only channels with ABS(temperature) greater
than the stack rms value (.rms) in calculating
all moments.

in clip:disp:2		Use only channels with ABS(temperature) greater
than twice the stack rms value (.rms) in calculating
the second moment (velocity dispersion).

DESCRIPTION:

Integrate the spectrum in stack 1 over a given horizontal interval.
The results in horizontal plot units are printed unless suppressed by
the 'dp:' flag (a header is also printed).  The result in K*Km/s is put
in the header variable 'area1' and the expected error in the area based
on the rms is put in 'arerr1'. The horizontal interval is specified in
horizontal plot units.

The centroid (first moment) is also calculated (horizontal value at which half
of the integral is reached).  The value of the centroid is put in the header
variable 'vcent1'.  This integration may include fractional channels at each
end.

The dispersion (second moment) is calculated as:

disp = sqrt[SUM(T_i(v_i-vcent)^2)/SUM(T_i)]

where T_i and v_i are the temperature and velocity of the i-th channel,
respectively. The result is put in fwhm1. Note for a purely Gaussian line,
the true full-width at half-maximum is sqrt(8ln(2)) times the dispersion.

Clipping levels (clip:) are applied to the moment calculations such that
channels with values between -(clip*.rms) and +(clip*.rms) are not used.
Thus it is important that the value of .rms is correct.  The default clip
levels are 0 for area and centroid (zeroth and first moments) and 1 for
dispersion (second moment). Since the centroid is calculated directly
from the area, it always takes the same clip level as the area.

ERRORS:

If the range of integration extends outside the stack, you will be warned.
If you agree to continue, no more of those warnings will be given on the same
command line.  The computed values will be based on the portion of the range
inside the limits of the stack.

If the limits of integration are completely outside of the stack, a similar
set of warnings will be given, but the value returned will be DRAGON (.DR).

If the square of the second moment is negative, .fwhm will be set to DRAGON.
This usually means the clip level was too low or that the integration
limits have been poorly chosen.
```