Comprehension versus speed
Reading comprehension is the ability to grasp what a text says and means: the topic, the author's points, supporting evidence, and important details. This page focuses on that skill. A timer may show while you read, but your score is based on quiz accuracy, not words per minute.
If you also want a paced WPM result with a comprehension check built in, use the separate reading speed test. Together, the two tools give a fuller picture of how you read.