Search Iranian Rial and click on Max above the chart.
Iranian Rial to Pound Sterling:
Why did the Iranian Rial peak suddenly on August 1st 2014?
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That data is just a spike that should be excluded but google finance has little (to no) incentive to fix data quality issues.
For example, CEIC reports that the exchange rate reached an all-time high of 44,070.000 IRR/USD in Jul 2018 and a record low of 1,439.000 IRR/USD in Oct 1992. This is against the USD - but unless GBPUSD moved like depicted in the chart, the exchange rate will be in line with the cross exchange rate.
IRR is usually quoted as shown above, and not as shown in the screenshot of the question (which is the inverse). It also does not matter much though, because it will more or less be the inverse of the rate. On Bloomberg, there is also no spike on that day.
In any case, if the outlier is so large, it is thankfully easy to determine it is a bad data point. It is a lot more difficult in cases that could make sense in theory. Data quality is a huge problem as Nick Patterson states (the whole podcast starts at 16:40, his discussion about his job at Renaissance Technologies starts at 29:55 - a sentence before that is also helpful). He is explaining that at his hedge fund, they had 7 Phd's just cleaning data and organizing the databases.
On August 1st 2014 violence shatters Gaza cease-fire hours after taking effect Israel and Hamas agreed to a 72-hour humanitarian cease-fire starting Friday, but the kidnapping of an Israeli solider and heavy exchanges of fire two hours after the truce took effect unraveled it.