A scale is a series that climbs up or down. Think of scaling, or climbing, a mountain; a musical scale: do-re-mi-fa-so-la-ti-do; or a scale you weigh yourself on––it counts up the pounds one after another after another.
Scale can be a ratio too––when maps are drawn "to scale," that means one mile of real road might translate to one inch of road on the map. Even fish scales can be understood this way––they repeat the same shape row after row after row. You can also rate something using a scale: "How much do you love pizza? Rate it on a scale of one to ten, with one being blech and ten being amazing."