Super had this idea and asked if it was possible to make and it had to be adjustable . We have a blind hill at one off the holes at the Old Course . We tried the greens sentry for a number of years but found it troublesome at times especially on week - ends if the battery died . I came up with this design and it has worked well for the past 3 seasons . Basically you view in the mirror before teeing off to see if the group is past the up to 250 yrd marker .