gradation; scale markings
Refers to the lines or marks on a measuring instrument such as a thermometer, ruler, or gauge. Often used in technical or everyday contexts when talking about reading a scale.
Read the gradations on the thermometer.
この定規は度盛りが細かくて見やすい。
This ruler has fine gradations and is easy to read.
Compound of 度 (degree) and 盛り (marking, from 盛る 'to heap up, to mark'). The exact historical derivation is uncertain, but the word transparently refers to degree markings.