  Various beam-based methods are widely used for machine study and accurate
tuning. Beam closed orbit (CO) responses are routinely used worldwide for
magnetic elements alignment and lattice correction. The paper presents the
beam-based field mapping technique, applied for measurement of pulsed septum
magnet stray field at VEPP-2000 electron-positron collider. Relatively slow
pulse of weak leakage field disturbs the CO allowing detecting field
longitudinal integral. While scanning with transverse coordinate in wide range
one can measure the field map of the localized perturbation at machine in situ.
