Sorry guys, been busy working ( and shooting) crazy hours.

Ernie, it's for 'known distance' long-range shooting.
Typically 600+ yards (up to about 1/2 mile) is considered long-range, with longer distances getting names like ultra, extreme, etc.

1/2 mile and longer shots are getting really tough to spot even with really expensive spotting scopes.
For known distance shooting (paper or steel targets) it makes sense to set up a wireless camera system and observe the shoots on a monitor/tablet.