What's the difference between a serial number and a product key?

Product keys are very similar to serial numbers as both are used to activate the Golden Software product.

Towards the end of 2016, Golden Software made a change to the way some of our products are licensed. If you purchased either Surfer or Grapher prior to December 2016, you most likely have a serial number. If you purchased after December 2016, you will have a product key. 

Product keys are in the form XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

Serial numbers are in the form XX-XXXXXX-XXXX