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diff --git a/noao/digiphot/apphot/fitsky/aphgmsub.x b/noao/digiphot/apphot/fitsky/aphgmsub.x
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+# AP_HGMSUB -- Procedure to subtract a point from an existing  histogram.
+
+procedure ap_hgmsub (hgm, nbins, z1, z2, skypix)
+
+real	hgm[ARB]		# histogram
+int	nbins			# number of bins
+real	z1, z2			# range of histogram
+real	skypix	               	# sky value
+
+int	bin
+real	dh
+
+begin
+	if (skypix < z1 || skypix > z2)
+	    return
+	dh = real (nbins - 1) / (z2 - z1)
+	bin = int ((skypix - z1) * dh) + 1
+	hgm[bin] = hgm[bin] - 1.0
+end
+
+
+# AP_HGMSUB2 -- Procedure to subract points from the accumulated sums
+# and the existing histogram.
+
+procedure ap_hgmsub2 (hgm, nbins, z1, z2, skypix, sky_zero, sumpx, sumsqpx,
+	sumcbpx)
+
+real	hgm[ARB]		# histogram
+int	nbins			# number of bins
+real	z1, z2			# range of histogram
+real	skypix	               	# sky value
+real	sky_zero		# sky zero point for moment analysis
+double	sumpx			# sum of the sky pixel values
+double	sumsqpx			# sum of the squares of the sky pixel values
+double	sumcbpx			# sum of the cubes of the sky pixel values
+
+double	dsky
+int	bin
+real	dh
+
+begin
+	if (skypix < z1 || skypix > z2)
+	    return
+	dsky = skypix - sky_zero
+	sumpx = sumpx - dsky
+	sumsqpx = sumsqpx - dsky ** 2
+	sumcbpx = sumcbpx - dsky ** 3
+	dh = real (nbins - 1) / (z2 - z1)
+	bin = int ((skypix - z1) * dh) + 1
+	hgm[bin] = hgm[bin] - 1.0
+end