With the data, we can simply calculate the kd value by using following equation.
$$\ce{A + T<-->T[K_{on}][K_{off}]AT}$$
$$k_{on}[A][T]=K_{off}[AT]$$
$$K_A= \frac{1}{K_D}=\frac{K_{on}}{K_{off}}=\frac{[AT]}{[A][T]}$$
By using the data, we can compare our affinity with the others' to ensure our binding affinity is outstanding.
Besides we used the equation
$$V=V_{max}\frac{[P]}{K_d\times{[P]}}+M\times[P]$$
As we know the aptamer has the ability to bind with non-specific region.