PC-Driven DSO Adaptor Mk2 (May/June, 1994): To improve the stability and calibration of the instrument, especially when making measurements with 'DC'input coupling, the following modification is suggested so that R35 (1k) is included in the negative feedback loop around U8a. Cut the PCB link between pins 1 and 2 of U8a, and use a short length of insulated hookup wire to connect pin 2 to the 'other end' of R35 -- i.e., the end connecting to C25, R6, R14 etc.