Wacom Intuos Pro - Screen Calibration

Hi, I have recently purchased the Wacom Intuos Pro - this is for one specific job within my work.  

Basically I apply graphics, crystals, embroidery etc to pattern pieces.  It's difficult to draw some of the shapes and therefore I have purchased the Wacom to trace round the shapes and then I know the exact area I have to work with.  

Here is the problem ..... When I trace round the pieces they appear around 10 x the size of the actual pieces and I then have to measure and scale down. 

Does anyone know how to calibrate the screen so what I draw is to actual size on the screen?