Consider a pair of overlapping vertical aerial photographs taken from a flying height of 665 m above a point A on the ground, with a camera having a focal length of 152.4 mm. The height of the point A above the mean sea level is 535 m. The parallax bar reading of the point A as measured from the photographs is 10.96 mm. Assuming the air base to be 400 m, the parallax bar constant is _________ mm.