http://www.zilog.com/docs/ez80/wp0001.pdf

Page 4, "The best way to avoid ESD damage is to keep ICs at the same potential as their
surroundings. The logical reference potential is ESD ground. The first and most
important rule in avoiding ESD damage is to keep ICs and everything that come in
close proximity to them at ESD ground potential. There are four supplementary
rules that support this first rule:"

"Any person handling the ICs should be grounded with either a wrist strap or ESD-
protective footwear used in conjunction with a conductive or static-dissipative floor
or floor mat."

Page 5, "The work surface for device handling,processing,testing,and so on,should be
made of static-dissipative material and connected to ESD ground"

Look at the picture on page 5, the floor mat and the work surface are to share a common ground.