This isn't how the Snap-On dude would do it...but it should get you close. It would be better to use a more controlled method to pull on the wrench handle. And the accuracy depends on how accurate the scale is. Same thing with using weights....if it ain't certified, it may not be right!
https://www.youtube.com/watch?v=XaqBA-xSGbc
The other option would be to contact Kobalt and ask them who would service/calibrate the wrench.
Hope that helps.
Mike