If you would like to calibrate the Screen Tracing Paper's units to match the drawing you're measuring then follow these instructions:

1. Click 'New' to create a new sheet.

2. Make sure 'Pixels' is selected in the 'Units' dropdown.

3. Click the 'Add' tool.

4. Click on the edge of the item you want to calibrate from, which should be a known distance.

5. Move the mouse to hover over the end of the item that you want to calibrate, but DO NOT CLICK.

6. At this point note the Circumference readout, which will be the distance in pixels of the item you want to calibrate from.

7. Click the 'Configure' button, the 'Configure Custom Units' popup will open.

8. Click 'Add Unit'

9. Type a descriptive name under 'Unit Name'

10. In the 'Number of Pixels' box enter the exact number you measured and noted earlier.

11. In the 'Length in Units' enter how many real life units the item is that you calibrated from, for example, if it is 3 feet then enter '3'.

12. Click 'OK'