When InstaRate starts up, it shows just the weight being read off the scale. There are several options on this screen:

Calculate Shipping Rates expands the window to show Canada Post rate calculation (see below).

Read Scale Continuously reads the weight off the scale every second, keeping the display in sync with what the scale says.

Read Weight from Scale reads the current weight off of the scale.

Weight is displayed in either pounds or ounces, and is used for rate calculation. You can click "Read Weight" above to fill this field with the current weight of items on the scale, or you can type in a weight.

From Postal Code is where you'll be mailing your package from. Some Canada Post rates are based on how far a package travels, so both To and From Postal Codes are required.

To Postal Code is the destination of your package.

Calculate looks up and displays the Domestic rates for your package.

Canada Post Mailing Rates are the current rates using the weight and postal codes provided.