The raw value of the figures seems scary (lowest value in 30 years, value of the pound dropped by 13%), but the reality is that after dipping very briefly to "the lowest level in 30 years" the GBP is currently about the same as it was in Feb this year and the value is down 4% from 2 weeks ago (not great, but nothing like a 13% downwards plunge).
Edit: Also worth noting, the FTSE is up from the start of the month, and roughly equal to what it was at the start of the week. Aside from a big dip and a bounce, it's literally like nothing happened [1].
0: http://www.xe.com/currencycharts/?from=GBP&to=USD&view=2Y
1: https://uk.finance.yahoo.com/echarts?s=^FTSE#symbol=^FTSE;ra...
That doesn't mean I'm not in a place to comment on what the market is doing - especially when it's a pattern that is repeated again and when major events occur.
2-3 months after the event will give a better idea of how the market values the decision to leave, rather than 1 day after.
A good 1/2 of the "tumble" was only added in the 10 days leading up to the decision [0].
I might not be making a killing, but someone is.
0: http://www.xe.com/currencycharts/?from=GBP&to=USD&view=1M
I don't know which way that trend will go, just that it will be clearer.
Edit: Also, keep in mind that all of this is in the context of the post of was replying to, trying to point out that the pound hasn't "tumbled".
You can't take the highest point from just before the result was known, and the lowest point from the few hours afterwards as a representative point of how the pound is doing in response to the news. If you put it in the context of a few weeks, or a few months, things are much more sane.
Despite all the sensationalism that the pound reached it's lowest point in 30 years, the pound is currently at the around the same price it was a few months back (currently only trading at a couple of cents lower than what it was back at the end of Feb - $1.37 vs $1.39).
Also, even if you don't know which way it'll go, you are making some claim about how the market will behave. It sounds like you're predicting a decrease in volatility? Ok, you can bet on that. If not that, then what? If you aren't predicting something that can be bet on, you aren't predicting anything at all.