You need to watch the 1 week charts then compare them.. Here is a good explanation of how trading works ...

Highest bid price
0.00065155 ETH
Lowest ask price
0.00060100 ETH
Spread
0.00005055 ETH
Maximum volume
8.99227066 AMB
You can buy 8.99227066 AMB for a price of 0.00060100 ETH at hitbtc and sell it for a price of 0.00065155 ETH at livecoin. This will make you a profit of 0.000454559281863 ETH!

Trade ICX/ETH from hitbtc to gateio
Cryptocoin ICX/ETH arbitrage opportunity seen at 14:20 February 26th 2018
Highest bid price
0.00469900 ETH
Lowest ask price
0.00439000 ETH
Spread
0.00030900 ETH
Maximum volume
97.13424183 ICX
You can buy 97.13424183 ICX for a price of 0.00439000 ETH at hitbtc and sell it for a price of 0.00469900 ETH at gateio. This will make you a profit of 0.03001448072547 ETH!

Trade HSR/ETH from kucoin to gateio
Cryptocoin HSR/ETH arbitrage opportunity seen at 14:20 February 26th 2018
Highest bid price
0.01141200 ETH
Lowest ask price
0.01125600 ETH
Spread
0.00015600 ETH
Maximum volume
4.29058184 HSR
You can buy 4.29058184 HSR for a price of 0.01125600 ETH at kucoin and sell it for a price of 0.01141200 ETH at gateio. This will make you a profit of 0.00066933076704 ETH!

Trade MDA/ETH from gateio to allcoin
Cryptocoin MDA/ETH arbitrage opportunity seen at 14:20 February 26th 2018