Apple Numbers has the ability to lookup stocks and currencies informations from Yahoo! Finance.
Since Yahoo! has listed BTC as a currency, it is easy to add its exchange rate into your Numbers spreadsheet.
Just insert in any cell the function
CURRENCY("currency-1";"currency-2";"optional attribute")
You can search for the correct currency symbols at https://finance.yahoo.com
For instance, at Yahoo! the Bitcoin exchange rate in dollars can be found as BTCUSD=X.
BTC would be currency-1 and USD would be currency-2
For your third attribute, Numbers automatically suggests “price." If you enter 0 or omit this item entirely, the cell shows the exchange rate of currency-1 to currency-2, expressed as currency-2.
Other currency attributes that you can track:
When you edit the formula, you can use any of these strings or numbers to show different pieces of data:
“name” (1): The currency codes of the specified currencies, shown in the formula for calculating the exchange rate.
“change” (2): The difference in the exchange rate at the close of trading on the two most recent business days.
“percent change” (3): The percentage change in the exchange rate’s two most recent closing prices.
“open” (4): The exchange rate at the opening of trading on the previous business day.
“high” (5): The highest exchange rate on the previous business day.
“low” (6): The lowest exchange rate on the previous business day.
“52-week high” (7): The highest exchange rate in the last 52 weeks.
“52-week low” (8): The lowest exchange rate in the last 52 weeks.
Some examples:
CURRENCY("BTC";"USD")
CURRENCY("USD";"BTC";"change")
Tracking currency history
If you want to track the history of a specific currency, use CURRENCYH. When you add the formula, you must define these attributes:
Currency-1: The currency code for the currency from which you’re converting. currency‑1 is a string enclosed in quotes.
Currency-2: The currency code for the currency to which you’re converting. currency‑2 is a string enclosed in quotes.
Attribute: An optional value specifying the currency attribute to be returned. Numbers automatically suggests "close." Instead of close, you can choose open, high, low, or any other currency attribute (see Currency attributes that you can track).
Date: The date for which you want the historical exchange rate information.