  We discuss price variations distributions in foreign exchange markets,
characterizing them both in calendar and business time frameworks. The price
dynamics is found to be the result of two distinct processes, a multi-variance
diffusion and an error process. The presence of the latter, which dominates at
short time scales, leads to indeterminacy principle in finance. Furthermore,
dynamics does not allow for a scheme based on independent probability
distributions, since volatility exhibits a strong correlation even at the
shortest time scales.
