Does iCustom slow down Strategy Tester and cause problems with Graph tab?

[Mikołaj Gogola]

Is it possible that iCustom function calls are slowing down my Strategy Tester? Is it somehow possible to prevent iCustom from drawing or something like this? I just want to grab values from indicator buffers.
I have also weird issue with Strategy Tester Graph tab. Graph tab is empty while Tester is running, but when its done everything pops up. Any ideas why it is happening?

[Marco vd Heijden]

Depends on how often it is called 

[Mikołaj Gogola]

Every tick.

[William Roeder]

1. EAs : Don't do per tick that you can do per bar, or on open.
   If you are waiting for a level, don't reevaluate, wait until price reaches it (or a new bar starts and you recalculate.)
   If you are waiting for an order to open or close, only look when OrdersTotal (or MT5 equivalent) has changed.
             How to get backtesting faster ? - MT4 - MQL4 programming forum

2. Indicators: Code it properly so it only recomputes bar zero (after the initial run.)
             How to do your lookbacks correctly.
   Or, reduce Tools → Options (control-O) → Charts → Max bars in chart to something reasonable (like 1K.)