等級 and 数値: a classification and a measured value
Distinguish a grade classification from a numerical measurement. Even a numbered grade does not become a measured length or weight with a physical unit.
等級 classifies quality
等級, read とうきゅう, means grade or class. 品質の等級によって果物の値段が異なる。 says that fruit prices differ according to quality grade.
The grade is a quality classification. The sentence does not supply grade names or a specific price difference between them.
数値 records a measurement
数値, read すうち, means numerical value. 測定した数値を表に入力しました。 says that someone entered the measured values into a table.
For a length measured in centimeters or a weight measured in grams, record the value with its unit. A number used in a grade name is not automatically such a physical measurement.
Classification does not describe physical growth
検査の結果、この製品は一つ上の等級に分類された。 says that the inspection resulted in this product being classified one grade higher. It does not describe an increase of one unit in the product’s length.
Measured values may be used to assign a grade, but the classification and the measurements themselves are different items. Read the order of numbered grades according to the relevant classification rules.
Does being classified one 等級 higher mean the product grew one centimeter longer?
Show the answer and why
No. The statement gives a classification result. A change in length requires separate information with a unit and measured values.