The following calibration format can be used directly in 
IRAF.digiphot.photcal.invertfit. The instrumental magnitudes
mU, mB, and mV are -2.5*log(counts/s)+25.

For the these images, the average parameters for UBV are the following:
Airmass---1.245, 1.27, 1.3
Integration time (s)---600, 480, 180
Pixel scale (arcsec)---0.42, 0.42, 0.42

# Mon 11:39:32 13-May-2002
begin	UFIT
	status	0	(Solution converged)
	variance	0.001682525
	stdeviation	0.0410186
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		0.001682525
	msq		0.001009515
	rms		0.03177287
	reference	mU
	fitting		(UB+BV+V)+u1+u2*XU+u3*UB+u4*UB*XU
	weights		uniform
	parameters	4
		u1	(fit)
		u2	(constant)
		u3	(fit)
		u4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		1.688987
		0.4
		-0.1248714
		0.
	errors	4
		0.01860653
		0.
		0.02560335
		0.

# Mon 11:39:55 13-May-2002
begin	BFIT
	status	0	(Solution converged)
	variance	3.811201E-5
	stdeviation	0.006173493
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		3.811201E-5
	msq		1.905601E-5
	rms		0.004365318
	reference	mB
	fitting		(BV+V)+b1+b2*XB+b3*BV+b4*BV*XB
	weights		uniform
	parameters	4
		b1	(fit)
		b2	(constant)
		b3	(fit)
		b4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		-0.150537
		0.3
		-0.009756085
		0.
	errors	4
		0.004957617
		0.
		0.005855678
		0.

# Mon 11:40:17 13-May-2002
begin	VFIT
	status	0	(Solution converged)
	variance	4.978733E-4
	stdeviation	0.02231308
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		4.978733E-4
	msq		3.319155E-4
	rms		0.01821855
	reference	mV
	fitting		V+v1+v2*XV+v3*BV+v4*BV*XV
	weights		uniform
	parameters	4
		v1	(fit)
		v2	(constant)
		v3	(fit)
		v4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		-0.2973222
		0.2
		0.03156269
		0.
	errors	4
		0.01709772
		0.
		0.02092936
		0.