In a military context, especially by the Finnish Non-Linear Artillery of The Continuation War, the Fire Correction Circle or (Fire) Correction Converter Dial is a fully mechanical auxiliary device which was constructed of plywood and transparent plastic and which used to be used to calculate targeting values for non-linear artillery and mortars. By using a Correction Circle the artillery observer is able to report the necessary fire corrections to the unit firing without knowing exactly where the unit is firing from.