Sentence:  The original electrocardiograph primarily indicates irregularities in the heartbeat , but today 's techniques allow <WSD>exact</WSD> 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:  (of ideas, images, representations, expressions) characterized by perfect conformity to fact or truth; strictly correct