can any one explain please why the monthly low for GBPUSD displayed in Market Milk is quite a bit different from what my MT4 chart is displaying? Im using Oanda MT4 and also selecting Oanda as the price source in Market Milk. The weekly high/lows are slightly different but the monthly low seems quite a large difference.
Did you check the price source? I think you can change it to match your broker’s but I don’t think they have a lot of brokers in there. 
This trading strategy is called arbitrage, It’s illogical for the same asset to trade at different prices, so eventually, the two prices must converge into one price.