Based on the coinmarket cap api, how do they calculate the bitcoin percent change I am trying to figure out how coinmarketcap calculates the bitcoin percent change for other coins. For example on ethereum:



I'm trying to figure out how they calculate that bottom BTC percent change 3.85%.

Their api (https://api.coinmarketcap.com/v1/ticker/?limit=100) spits out this data:

{
    "id": "bitcoin", 
    "name": "Bitcoin", 
    "symbol": "BTC", 
    "rank": "1", 
    "price_usd": "8397.08", 
    "price_btc": "1.0", 
    "24h_volume_usd": "8190950000.0", 
    "market_cap_usd": "141531834530", 
    "available_supply": "16854887.0", 
    "total_supply": "16854887.0", 
    "max_supply": "21000000.0", 
    "percent_change_1h": "-0.51", 
    "percent_change_24h": "1.0", 
    "percent_change_7d": "-1.88", 
    "last_updated": "1518191066"
}, 
{
    "id": "ethereum", 
    "name": "Ethereum", 
    "symbol": "ETH", 
    "rank": "2", 
    "price_usd": "846.675", 
    "price_btc": "0.101377", 
    "24h_volume_usd": "3096660000.0", 
    "market_cap_usd": "82559453770.0", 
    "available_supply": "97510206.0", 
    "total_supply": "97510206.0", 
    "max_supply": null, 
    "percent_change_1h": "-0.2", 
    "percent_change_24h": "4.14", 
    "percent_change_7d": "-5.14", 
    "last_updated": "1518191052"
}


The first number is stated in this "percent_change_24h": "4.14" but they dont show how they came up with that second number ( 3.85% ).

Is there some formula I can create with the data they provide?

Thanks
Well, you have all the information you need:


Compute the price of your coin 24h ago (in USD)
Get the price of the bitcoin 24h ago (in USD)
Compute how much bitcoin your coin was worth in BTC 24h ago using the two previous results
Compare with the current BTC value of your coin


Done :)