如何利用 abitrage 获得优势？ (how to use abitrage for an advantage?)

Hi i have discovered a way to find price for another currency

i. eur/gbp x gbp/usd = price of eur/usd well it lags a little 3 or 4 pips

but considering broker spreads

your still at a lost well ok you might get into profit faster if your trading is successful

but you want really is a secure profit

i.e if i know that the price of the eur usd was going to go to a certain level with a move of 20 pips i know it was going to make i might buy and sell it because i know it will make them pips.

however sadly it is only a few pip differences

but has got me thinking

how else can it be used?

maybe like pivots support resistance

or is there better combinations
nth term thing?

or just another dead end?