There is also an earlier model 533 which is similar but has different grid signal levels and different switch settings. Sensitive shorts tests lights neon bulb when there is either a direct short between elements or high resistance leakage. Noise test is useful for detecting microphonic tubes. Gas test is used to determine if any stray gas molecules are present inside the tube. This is especially helpful when checking amplifier tubes.
Gassy tubes cause problems with bias adjustments.
Built in roll chart has settings for most popular tubes Obsolete Tube and Foreign Tube Roll Chart Supplement books are included with this tester.