Yes, leave set at zero, this angle change will give the true distance to the target, above or below horizontal reduces the true distance,(corrected for gravity) type in your bullet weight, coefficient, available from the manufacturers web site, the muzzle velocity, my .308 hits about 2700fps with 155's, experiment with the wind speed, target speed should be zero.
Have fun,
PV.
P.S.
http://www.snipertools.com/aci.htm