I've never noticed this website before, it seems amazing, nice job!
1. We collect pieces of data from all available exchanges over the Internet. Each piece consists of
nominated fiat currency
last trade price
current lowest ask
current highest bid
24h sliding window trading volume
For multicurrency exchanges like LocalBitcoins we collect multiple pieces, separately for each currency.
This data is collected roughly every minute, and cycle time may slightly vary depending on the load time for various exchanges.
2. When all data is collected we calculate weighted averages within each currency according to trading volumes. Weighted averages are calculated for last price, bid and ask separately.
These weighted averages are shown on site as currency markets data.
Of all globally recognized currencies only around a dozen are shown in the market area. This is because we recognize as markets only currencies that are directly traded to BTC anywhere in the world.
3. Global average is calculated using fiat exchange rates, so it can be shown in nearly any fiat currency. To calculate global average we choose a target currency (USD as example).
Then we convert each market's weighted average into target currency using fiat exchange rates provided by openexchangerates.org.
4. Then the global weighted average is calculated using each market's average converted into target currency.
Each market's total trading volume is used as weight for calculation.
5. Finally global weighted average in formed, in any convertible world's currency.
