There are two tables, one shows the live bitcoin price in various currencies. For example:
Dollars US$601.01
Euros E 541.06
...
The second table, is 'My Balance'. For example:
Bitcoin 0.5
Dollars 300.50
And since the start of the thread, the quantity of bitcoins has gone up by 0.00000224.
I think your currency is in dollar that is why the bitcoin value is fluctuating. This is the possible scenario, since your currency is in dollar, your possible bitcoin value is displayed. When exchange rate changes, so is your possible bitcoin value and vice versa if your currency is in BTC, your possible dollar value will fluctuate depends on btc exchange price.