真的畫出來的那條線
這一類就是核心畫面的字面版：一條看得見的線，先畫好，其他東西再照著它擺、照著它量，或者靠它分出裡外。
noun · B2
A straight line that is marked out first and then used to measure or set out everything else, for example when building something, measuring land, or drawing a plan.
基準線
核心畫面
Think of a line laid down first, before anything else happens. Nothing is built, drawn or judged until that line is there. Once it is, everything else takes its position from it: you measure out from it, you line things up on it, you decide what is inside it and what is outside it. The line itself is nothing special; its whole value is that it came first and it does not move. Every other meaning of the word, on a court, on a page, or in a column of numbers, is that same fixed first line doing that same job.
可以想成一條「先放下去的線」。東西還沒蓋、還沒畫、還沒判之前，這條線先在那裡。有了它，其他東西才有位置：距離從它量起…更多收起
可以想成一條「先放下去的線」。東西還沒蓋、還沒畫、還沒判之前，這條線先在那裡。有了它，其他東西才有位置：距離從它量起，東西照它對齊，界內界外靠它分。這條線本身沒什麼特別。它的價值只在兩件事：它先到，而且它不動。球場上的線、頁面上的線、報表裡拿來比的第一組數字，做的都是同一件事。From the word’s history
Wiktionary analyses the word as base + line: the line that acts as the base for something else.
維基詞典把這個字分析成 base（底、基礎）加 line（線），也就是「給別的東西當底的那條線」。這正好對上它今天的用法：不論是地上的線還是報表裡的第一組數字，作用都是「當底」。
Wiktionary entry for 'baseline' (packet etymology_text: "From base + line.")
Two branches
拿來比的那個起點
線從地上搬進數字裡。看不見了，但工作一樣：先定下來、不再改，之後每一筆都從它算起。這是教學上的聯想，把兩邊接起來幫助記憶，不是在說歷史上誰先誰後。
noun · B2
A first measurement, number or fact that is written down at the start and kept, so that later measurements can be compared with it and you can see how much has changed.
基準值