The means of g 1l l 1 and g 2l l 2 are l 1 and l 2 respectively. Let the standard deviations be s x and s y respectively. For given estimationsl l 1 andl l 2 , assuming that distributions are normal, it follows from the analysis in [20, 21] that the boundary of the confidence ellipse for a given confidence level z c would be defined by