On one end of the ruler a CR1220 battery feeds the 18F43K20 which is performing the logic operations using buttons and LEDs. Of course the truth tables are printed on the back silk-screen, but ...

If you want to show a ruler on your computer screen, here is how you can do that. You can use PowerToys or other third-party tools to display a ruler on your screen.

• Take your ruler and lay it flat on a table or desk. How many inches on the ruler can you nudge over the edge of the table before it falls off? Think about our hypothetical seesaw from earlier.