Located on Throgmorton Street in the shadow of the old Stock Exchange, which, incidentally is currently being developed by Hammerson from the archetects Grimshaw the new Stock Exchange is now near St Paul's in Paternoster Square. I guess being located next to the Stock Exchanged is where the pub name came from, arbitrage is a financial term for simultaneous purchase and sale or something like it.  Anyway, back to the pub, upstairs is tiny (downstairs was closed on my visit, due to lack of customers I was told, since there was only one bar man it would have proved difficult to have both open so I'm guessing here, but the lack of custom is normal) despite it's size the half a dozen men puffing away on there cigarettes  managed to fill the air with smoke, I could feel my chest tighten as I breathed the air.  They have no beer on tap, just lagers and I think possibly Guinness , I had '1664' costing £3.00.  The upstairs bar is pretty rough and would greatly benefit from a refurbishment the smoking ban due in July this year will also help the atmosphere.  Ironically the first non smoking bar in the City is just a couple of doors along the street and was busy.