**Table 2:** "Inside correlations'' between gradients from various sources, used in the estimation of probable errors in each dataset. The impartial correlation Y=pX+a is given.
X	Y	S	N	p	a	$\rho$	$\sigma$
$\Delta _{BV}$	$\Delta _{UB}$	I	39	$2.10\pm .23$	$-.005\pm .005$	.75	.029
$\Delta _{BV}$	$\Delta_{VI}$	I	39	$1.12\pm .16$	$.022\pm .003$	.51	.020
$\Delta _{BV}$	$\Delta_{BR}$	I	37	$1.33\pm .10$	$.004\pm .002$	.90	.012
$\Delta _{BV}$	$\Delta_{VI}$	G	32	$1.39\pm .30$	$.030\pm .006$	.45	.035
$\Delta_{BR}$	$\Delta_{UR}$	P	25	$2.00\pm .29$	$.083\pm .010$	.73	.051

(1) X variable; (2) Y variable; (3) S source reference abbreviated as I for IMP02 (enlarged from several OHP measurements), G for Gal94, P for Pal90 and Fal89 merged; (4) number of objects N after rejection of outliers; (5) slope p; (6) zero point a; (7) coefficient of correlation $\rho$ ; (8) dispersion $\sigma$ .

Source LaTeX | All tables | In the text

	1 Introduction
	2 Collecting the gradients
	3 Properties of colour gradients
	4 Simulated datasets of colour gradients
	5 Concluding summary
	References