bar.TickVolume != no onTick event is envoked

Hi there,

i observed that bar.TickVolume is about 40% higher than the event Action<TicksTickEventArgs> Tick is triggered per period. My understanding so far is that the tickvolume in forex is the number of price changes of an instrument per period, yet OnTick or Calculate show distinctly lower numbers. 

protected override void Initialize()
{ 
_Ticks = MarketData.GetTicks(SymbolName);
_Ticks.Tick += OnTick; 
}

private int lastIdx = -1;
private int noTicksCalculate = 0;
private int noTicksOnTick = 0;

public override void Calculate(int index)
{
if (Bars[index].OpenTime > Time.AddMinutes(-6))
if (lastIdx != index)
{
Print(index + " ticksstat: bar.tickvolume: " + Bars.Last(1).TickVolume + "/ calculate:" +
noTicksCalculate + "/ onTick:" + noTicksOnTick);
lastIdx = index;
noTicksCalculate = 0;
noTicksOnTick = 0;
}

noTicksCalculate++;
}

public void OnTick(TicksTickEventArgs Args)
{
noTicksOnTick++;
}

Sample output:

28/07/2023 15:01:00.151 | 7177 ticksstat: bar.tickvolume: 182/ calculate:114/ onTick:113

Question: I expect barTickVolume, the number onTick is called, and the number Calculate-1 is called to be equal.. 

Thanks,
Armin