Scientists take more than one measurements because they want to make sure that their results are fairly accurate answer, result, or/ and explanation on a subject.
Reason: If a scientist just used one measurement or used even one testing group then in the near future, people might use that ONE measurement or testing group to prove questions. .
In actuality, using more than one measurements can help you go for a more precise answer. It is better to use more than one measurement or testing group that way you may have a more wide explanation of why something is that way.
For example, if a person wants to know why a softer ball(like a tennis ball) bounces higher than something like a box then the person will use more than one measurement. This will include the height of the bounce, the volume of the items used, the force of gravity on the object, and some other things.
(Hope this helps you better understand :) )
