A measurement amount (like weight, temperature or money) can be inserted in the text of a note using the Add Features - Add Chart point menus. All the notes having this measurement unit in them will then be able to plot a time-based Chart in the Search/Chart screen of the app.
The first step in using Charts is to define one in the Options screen. The Chart units defined in the Options screen will then be available in the Add Features - Add Chart point menu of a note in edit mode.
You can add multiple Charts with different types of units. They can be shown selectively on the same Graph. The Graph image and the Graph data can be saved and exported from the Chart screen.