public decimal CalculateZoneCost(decimal radius, bool relink)
{
// linear cost on radius.
return (relink ? TradeZoneRelinkRatio : 1m) * (((radius - TradeZoneMinRadius) / (TradeZoneMaxRadius - TradeZoneMinRadius) * (TradeZoneLicenceCostMax - TradeZoneLicenceCostMin)) + TradeZoneLicenceCostMin);
}