pro use_vlth, value_out, set=set, noset=noset

common f_vth_com, use_vlth
checkvar, use_vlth, 0
if n_elements(set) or n_elements(noset) then begin
checkvar, set, 1
checkvar, noset, 0

if set then use_vlth=1 else use_vlth=0

if noset then use_vlth=-2
endif

value_out = use_vlth
end