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---1.06, 1.03, 1.02
Integration time (s)---1000, 900, 600
Pixel scale (arcsec)---0.61, 0.61, 0.61

# Wed 09:34:34 15-May-2002
begin	UFIT
	status	0	(Solution converged)
	variance	0.004595971
	stdeviation	0.06779359
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		0.004595971
	msq		0.00434064
	rms		0.06588353
	reference	mU
	fitting		(UB+BV+V)+u1+u2*XU+u3*UB+u4*UB*XU
	weights		uniform
	parameters	4
		u1	(constant)
		u2	(fit)
		u3	(constant)
		u4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		3.517
		0.4119617
		-0.0923
		0.
	errors	4
		0.
		0.008613604
		0.
		0.

# Wed 09:34:47 15-May-2002
begin	BFIT
	status	0	(Solution converged)
	variance	6.823423E-4
	stdeviation	0.02612168
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		6.823423E-4
	msq		6.539114E-4
	rms		0.02557169
	reference	mB
	fitting		(BV+V)+b1+b2*XB+b3*BV+b4*BV*XB
	weights		uniform
	parameters	4
		b1	(constant)
		b2	(fit)
		b3	(constant)
		b4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		1.706
		0.2600327
		0.0255
		0.
	errors	4
		0.
		0.003005073
		0.
		0.

# Wed 09:35:03 15-May-2002
begin	VFIT
	status	0	(Solution converged)
	variance	1.148043E-4
	stdeviation	0.01071468
	avsqerror	1.
	averror		1.
	avsqscatter	0.
	avscatter	0.
	chisqr		1.148043E-4
	msq		1.098128E-4
	rms		0.01047916
	reference	mV
	fitting		V+v1+v2*XV+v3*BV+v4*BV*XV
	weights		uniform
	parameters	4
		v1	(constant)
		v2	(fit)
		v3	(constant)
		v4	(constant)
	derivatives	4
		0.1
		0.1
		0.1
		0.1
	values	4
		1.542
		0.1254764
		-0.003
		0.
	errors	4
		0.
		0.001274713
		0.
		0.