Below is an interactive odometer built with Web Sketchpad. Press each of the ‘+’ keys and observe their effect on the odometer’s value. Also notice how your button presses are tracked in the table below the odometer.

I built this model as a way to support students’ development of place-value concepts. Here are two ideas for how you might use it:

- Pick a target number and ask students to name different combinations of button presses that will land the odometer at the target. To reach 100, for example, we might combine 9 tens with 10 ones or 7 tens with 30 ones. For larger targets like 1,000, there are lots of possible answers.
- Press ‘Hide Odometer.’ Then, press the various ‘+’ buttons multiple times. Ask students to determine the hidden value of the odometer based on the information in the table. For example, 3 hundreds, 5 tens, and 2 ones is 352. A more challenging problem is to convert 12 hundreds, 15 tens, and 18 ones to 1,368. Students love creating these puzzles for each other because it’s fun to press the buttons, and the more they press, the harder the problem!

In my next post, I’ll share another odometer that has ‘–’ as well as ‘+’ buttons. The inclusion of ‘–’ buttons leads to some very interesting problems.

*An annotated list of all our elementary-themed blog posts is here.*