The Set-up at Fluke (IMAGE) National Physical Laboratory Caption This is a sampling oscilloscope (model HP54750A) being used to measure the AM of a 9640A. A second 9640A is used to supply a reference signal. Credit NPL/Fluke Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.