Abstract: Method and apparatus for logging a well during drilling operations to record drilling fluid gas and rate of penetration as a function of depth. The system comprises elements for producing a succession of depth signals in response to applied inputs and applying the depth signals to a variable output scaler. The scaler is comprised of a set of retriggerable monostable units, each having different time constants. The scaler output is employed to actuate the index drive of a recorder to provide a desired logging scale. The scaler output is also employed to reset a bank of digital counters which are pulsed by clock signals from a time base generator. The values in the digital counters are applied to a digital-to-analogue converter. The output from the digital-to-analogue converter is recorded as a function of the depth index along with the gas signal. Latch elements are interposed between the digital counters and the converter.