Abstract: A method of and apparatus for determining the spacing between a ribbon of hot glass and a coater extending over the ribbon for forming a coating thereon by chemical vapor deposition. Position sensors are affixed to the coater at selected positions therealong. The sensors include an annular outlet through which a compatible gas is discharged against the glass surface from a position closely adjacent the surface, and a central opening for measuring the back pressure resulting from impingement of the gas against the glass surface. The back pressure is a function of the distance of the annular outlet from the glass surface, and the size of the annular passageway and rate of gas flow therethrough are such that a smooth well-defined pressure-versus-distance curve is produced for the range of distances within which the coater is intended to operate. Comparison of observed pressures with pressures at known distances indicate the sensor-to-glass, and hence the coater-to-glass, distance.