HP b2600 Reference Manual page 322

P
gluPerspective
Notes
Depth buffer precision is affected by the values specified for zNear and zFar. The greater
the ratio of zFar to zNear is, the less effective the depth buffer will be at distinguishing
between surfaces that are near each other. If r = zFar / zNear, roughly log
depth buffer precision are lost. Because r approaches infinity as zNear approaches 0,
zNear must never be set to 0.
See Also
glFrustum,
glLoadIdentity,
glMultMatrix,
gluOrtho2D
322
r bits of
2
Chapter 14