Abstract: An improved penetrometer includes a stationary ink delivery system and an improved photohead, which connects to a light source and a photodetector via two fiber optic cables. A solid state electronic circuit automatically controls the operation cycle of the penetrometer, with a single start button controlling all operations of the instrument. In particular, there is no need to reset the clock timer to zero or to adjust the 100% reflectance value prior to each test. A ratio meter displays the ratio of the current reflectance to the locked-in initial reflectance in real time as the test proceeds.