How do Professional Golf caddies measure distances to the hole during a tournament round?

QUESTION:
I havent seen any caddy carry a golf gps or one of those radar assisted measuring devices to calculate the distances to a particular hole. All they seem to carry is a notepad.. So do they have electronic devices to assist them and we just dont see them use it on television coverage or do they follow some other method?? Or is it a combination of both?? Really interested in knowing this..Thanks guyz..

ANSWER:

Answer by old man on the hill
that little note pad is actually a drawing of the hole with yardages from landmarks such as front of bunker, back of bunker, stream crossings, trees, etc to the front of the green. the drawing also includes the size of the green. the drawing may even include sprinkler heads and distances

in most pro tournaments gps systems are not allowed