  Using non chiral supersymmetry in 6D space time, we compute the explicit
expression of the metric the scalar manifold $SO(1,1) \times \frac{SO(4,20)
}{SO(4) \times SO(20)}$ of the 10D type IIA superstring on generic K3. We
consider as well the scalar field self-couplings in the general case where the
non chiral 6D supergravity multiplet is coupled to generic n vector
supermultiplets with moduli space $SO(1,1) \times \frac{SO(4,n)}{SO(4) \times
SO(n)}$. We also work out a dictionary giving a correspondence between
hyperKahler geometry and the Kahler geometry of the Coulomb branch of 10D type
IIA on Calabi-Yau threefolds. Others features are also discussed.
