An algorithm has been developed for fast analysis of a sparse multichord interferometer array, yielding peak density, Gaussian width, radial offset, ellipticity, and instability amplitude and frequency from line‐integrated density measurements. A nonlinear least‐squares fit is performed over many short time intervals, with independent variables reduced to one dimension. Assumptions of plasma rigidity and slowly evolving rotation rate are necessary to trade temporal resolution (on instability timescales) for spatial resolution across the moving plasma column. Results from the Tara tandem mirror experiment are shown.