This is a nicely designed site and some good data feeds. There is a big difference between spread, and arbitrage. Critically, any attempt to track arbitage needs to watch the orderbook rather than the last-trade-price. Ironically, the bid/ask spread on the same exchange isnt part of arbitrage. The difference between the total available bids on exchange A and the total available asks on exchange B (or vice-versa), is the opportunity.

I wrote and ran an arbitrage tracking site for a few years and eventually stopped because there did not seem to be viable way to take advantage of cross-exchange spreads. Sell-Move-Buy didn't work because moving coins took days. Having a pile of each kind of coin on each change is fast but defeats the point of arbitrage because the pile itself it subject to the price changes that arbitrage is made to avoid.

The chart below shows the result of looking at the orderbook of different BTC exchanges, seeing how much was actually offered at a winning price on other changes, computing the total, and taking into account exchange fees (more or less)

At 10:10pm there is a $16USD spike - probably between BTC-E and Gemini that lasted a short while (refresh rate was every 10 min) https://web.archive.org/web/20160219100013/http://cointhink....

I always thought the code could be generalized enough to look at any number of exchanges and coinpairs. I'll keep an eye on tokenspread, it looks like a good start!