Currency Trading Explained

How forex scalper checks out liquidity of the chosen pair?
That was my question.
If he judges by spread, what spread( like 1 , 1.5 …anything like that) would be considered as a liquid currency pair by the scalper?
(or)
Please Guide me, how to check whether the currency pair is highly liquid when i enter the trade…Please explain to me in detailed and simple way.
Thank you.
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http://compareexpertadvisors.blogspot.com/
It will also explain about the benefits of each type of expert advisor.
Currency Trading – Earn Daily Interest