b. Absorbing glasses, pyrometer lamp, and red filter 9 c. Microscope assembly d. The electrical circuit 3. Sources 3.1. Blackbodies a. Gold-point blackbodies b. Lesser quality blackbodies 3.2. Tungsten strip lamps a. Types of strip lamps b. Factors affecting the reproducibility of strip lamps 3.3. Other sources a. The carbon arc b. High-pressure arcs 4. Primary caUbration 4.1. Calibration at the gold point 4.2. Calibration above the gold point 4.3. Estimated accuracy 5. Secondary calibrations 19 5.1. Optical pyrometers a. Inspection and cleaning 19 b. Determination of the effective wavelengths 19 c. Calibration procedure d. Low-range calibration e. High-range calibrations 5.2. Tungsten strip lamps a. Calibration range b. Mounting and orientation c. The electrical system d. Calibration 5.3. Precision and accuracy 23 a. Definition of precision and accuracy 23 b. Statistical model for calibration errors 24 c. Uncertainties on certificates 24 d. Differences between the IPTS and TTS 25 6. Applications 25 6.1. Temperature measurements 25 6.2. Spectrical radiance calibrations using strip lamps 25 6.3. Secondary standards 26 6.4. Recommendations for achieving high accuracy and precision 26 6.5. Fundamental limitations 27 6.6. Photoelectric optical pyrometers 27 7. References