Sealey TA4000 Manual page 100

Instruction of the Ellipse Method
Sinθ = A/B or C/D, where θ = phase shift (in degrees) between the two signals.
From the formula above:
θ = ±arcsine (A/B) or ±arcsine (C/D)
θ must be in the range of (0~π/2) or (3π/2~2π) if the main axis of the ellipse is between
I and III quadrant, . If the main axis is at II and IV quadrant, θ must be in the range of
(π/2~π) or (π~3π/2).
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Original Language Version TA4000 Issue: 1 - 06/09/11