Sanborn Company. Sanborn Twin-Viso Models 60-300, 60-400, 60-1000. Instruction Manual. Table of Contents holds the following paragraph heads: Introduction, DC Preamplifier (Controls, Balance Adjustment, Calibration, Bias Adjustment), AC Preamplifier (Controls, Calibration, Decay Curve Adjustment), Applying the Input Signal, Testing and Replacing Calibration Cells, Power Supply Controls, and Positive Voltage Adjustment.