Source data can be accessed by drilling down into the underlying data screen.  Also, please see  the Row Lock and Row to Row Calculation articles which discuss among other articles how to use the underlying data screen.

To prevent Drill Down on an account, please see How Do I Prevent Users from Drilling Down on Accounts.  Disabling specific account drill down can be useful to prevent users form seeing the transaction details and also prevent accidental Drill Down on  high volume accounts that may result in system slow-down.

Data that can be drilled into displays per below in blue with an underline.  Click on the blue data and the display will change to the underlying data screen.  

In the below example the Basic Budget Entry screen is illustrated.  The summary data is displayed on the Basic Budget Entry/Dashboard screen.

By clicked on the blue account number the screen display moves to the Basic Budget Entry/Account Details screen per the below.  Please note that all the data fields on this screen related the 000-4100-00 which is the account that was drilled into.