**Table 2:** Observed and modeled quantities.
	Observed	Model
Single dish:
Velocity range^a (km s^-1)	270 $\pm$ 20	$\sim$ 280
EVN+MERLIN:
$\tau_{\rm North}^{b}$	$3.85\pm0.34$	3.58
$\tau_{\rm South}$	$4.30\pm0.12$	3.80
$\tau_{\rm East}$	$2.66\pm0.33$	1.20
$\tau_{\rm West}$	$2.26\pm0.21$	0.69
Global VLBI:
$\tau_{\rm South}$	>6.21	7.28
FWHM of peak spot (km s^-1)	$\sim$ 30	30

^a Velocity width of the 1667 feature at 10% of the peak flux density.
^b The effective opacities are $\tau_{\rm North} = {\rm ln}({\rm LCR}_{\rm North})$ , etc.

Source LaTeX | All tables | In the text

	1 Introduction
	2 Source properties and observations
	3 Clumpy ring model
	4 Modelling and results
	5 Discussion of maser properties
	6 Physical considerations
	7 Conclusions and future work
	Appendix A: Maser gain in clumpy media
	References