Slit positions with respect to the nebula and their reconstruction. The slit orientation is as read from the dial on the spectroscope. The value of m at the pulsar trace in the spectrum is taken as reference. The coordinate x‐axis (ξ) points to the west (right) and the y‐axis (η) points to the north (up). Star traces in the spectrum are noted, and the corresponding distances to the reference trace are marked as points along a line with a given orientation. Such points (e.g., the three black dots in the bottom image for slit orientation 0°) are transported in parallel until they correspond with some stellar feature in the image. The background image is a combination of three VRI filter images obtained at the Guillermo Haro observatory in Cananea by Čadež et al. (2001) in the stroboscopic mode to enhance the brightness of the pulsar.