Use scratch to make a usable tool

Open scratch.mit.edu and click "Create" to start a new Scratch project so you have a blank slate to work on.

Decide whether you will build a calculator or a timer and say your choice out loud so your project has a clear goal.

Write three features you want your tool to have on your paper so you know what to build first.

Draw a simple layout on your paper showing where the display and buttons will go so you have a plan to follow.

In Scratch make a new sprite and name it "Display" so you have a place to show numbers or time.

In Scratch create variables named DisplayText FirstNumber and Operator for all sprites so your code can remember numbers and the operation.

Make one number button sprite and add code so when that sprite is clicked it appends its digit to DisplayText (if DisplayText is "0" then set it to the digit) so numbers appear on the display.

Create digit buttons 0 through 9 by copying the number button and changing each label so you have every number to press.

Make operator buttons (+ - × ÷ or Start Stop for a timer) and add code so each operator button saves DisplayText into FirstNumber sets Operator and resets DisplayText to "0" so the tool knows what to do next.

Create an equals button and add code that checks Operator then calculates FirstNumber (operator) DisplayText and sets DisplayText to the result so your calculator gives answers.

Add a clear button and add code to set DisplayText to "0" and clear FirstNumber and Operator so you can start fresh anytime.

Test your tool by trying at least three different calculations or timing runs so you can see how it works in action.

Fix any bugs you find by editing the scripts then test again so your tool becomes reliable and reusable.

Save your Scratch project and write short usage instructions in the project notes so other people know how to use it.

Share your finished creation on DIY.org so other kids can see and try your useful tool.