Technical notes. 536. Disclosures on: Viscous damped wind vane, nonskid road or runway, regrooved pneumatic tire with removable inserts, device for radially positioning rotating wheel, method for fabricating precision waveguide sections distortion-cancelling loudspeaker system, cryogenic fluid density measurements system, controlled-atmosphere weathering device; editors, David Robbing and Alvin J. Englert.