Sentence:  The original electrocardiograph primarily indicates irregularities in the heartbeat , but today 's techniques <WSD>allow</WSD> exact measurements of the flow of blood through the aorta , dimensioning of the heart and its chambers , and a much more detailed study of each heartbeat . 
Meaning of the word marked with <WSD> tags:  make a possibility or provide opportunity for; permit to be attainable or cause to remain