On your trading platform you will observe Quotes like this
EXAMPLE of USDZAR
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Both these buy and sell Quotes are higher than the original Quotes set by Banks. Banks set Quotes, then Brokers Modify the quotes.
Original Quotes
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Banks says 1 USD equals to 17,10. but broker says 1 USD equals to 17.1233 when i sell and is 17.1433 when i buy
Calculations
Sell price - original price
17.1233 - 17,10 = 0.0233
the 0.0233 is commission for brokers when you choose to sell. it will differ when you buy.
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selling and buying price has more decimals than original price. those decimals are called pips.