US Patent 9943237 Analysis of direct and indirect heartbeat data variations

One method for measuring variability between direct heartbeat data and indirect heartbeat data includes: receiving first heartbeat data from an electrocardiogram over a period of time; receiving second heartbeat data from an indirect measure of heartbeat data over at least a portion of the period of time; calculating, by a computing device, a difference between the first heartbeat data and the second heartbeat data; and comparing the difference to determine a variation.