At the CERN SPS, the DsTau project has been proposed to study tau-neutrino production aiming at providing important information for future v, measurements. Precise measurement of the v, cross section would enable a search for new physics effects in v, charged current interactions. It also has practical implications for neutrino oscillation experiments. The dominant source of v, is the sequential decay of Ds mesons produced by proton interactions, whose uncertainty dominates current uncertainty in the v, cross section measurement. The project aims at reducing the systematic uncertainty from about 50% to 10% by measuring the Ds differential production cross section. For this purpose, emulsion detectors with a nanometreprecision readout will be used to detect small kinks of the Ds T decay. An emulsion detector has a position resolution of 50 nm, allowing for the detection of Ds T X double kinks in a few millimeter range.