significant, but we are not able to make better analytical approximation near cusps [@pejcha09].

The value of $s_0$ can be found by calculating the distance between the lens and the position of the second cusp projected onto the binary axis (point $X$ in Figure \[fig:geo\]). Basic geometry gives a value of $0.61$. It is equal to $s_0 - 1/s_0$ thus $s_0 = 1.35$. The distance between the projected position of the second cusp and the first cusp is $2\sqrt{q}/\left(s\sqrt{s^2-1}\right)$ [@han06] and in the analyzed case equals $0.126$. Thus the mass ratio is $0.0059$.

The values found using this analytical approximation are close to the results presented in Table \[tab:res\] especially when compared to the model without microlensing parallax and orbital motion. In the case of events perturbed by the cusps of planetary caustics, such calculations should be useful for starting values in model fitting.

[44]{} natexlab\#1[\#1]{}

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