A universal and reversible disposable ECG sensor positioning mask and method for use with electrocardiogram diagnostic equipment for left and right chest ECGs in which the mask has at least nine sensors, six of which can be used at any one time to provide up to four different sizes to accommodate varying sized human torsos. The novel blades twisted blades can be configured for 60\u2033 and 64\u2033 diameter fans, and have less blades than conventional flat type bladed fans having 4, 5 blades and have greater air flow and less power draw results than the conventional flat 54 inch fans. A switch selects between the first analogue video signal and the second analogue video signal as an output depending on a control signal based on the occurrence of said time window.