FXCM's current copywriter may have some sort of excuse for not knowing about this particular trick, because it doesn't work with the "ODL Powered by FXCM" brand of MetaTrader 4. Because of that I used my shiny new (and modestly funded!) live spreadbetting account with Smart Live Markets to demonstrate how to perform a partial close on those flavours of MT4 that support it.
Smart Live's minimum order size is 10 pence per pip, which is entered as a volume of 0.1 lots into the MetaTrader 4 client terminal. Earlier this morning I bought 0.2 lots of Cable at market:
A little later I sold 0.1 lots at a modest profit:
This resulted in two opposing positions in GBP/USD, one twice the size of the other:
Next I used MT4's "Close By" order type to merge the two positions into one 0.1 lot long position:
After I clicked on "Close" Smart Live confirmed that the two positions had been merged into a new, smaller, long position and informed me of the new order number. A partial close by another name:
At this point you may well want to go and try out this trick for yourself on one of your demo accounts. If you discover that your own MT4 broker, like FXCM, doesn't support this useful functionality you might also then scratch your head and ask yourself this question:
"Why on Earth not?"