Instruments - iOS Programming: The Big Nerd Ranch Guide - page 591

Each row in this table shows a single instance of Line that has been created. Select one
of the rows and check out the stack trace that appears in the Extended Detail area on the
right side of the Instruments window ( Figure 21.10 ) . This stack trace shows you where
that instance of Line was created. Grayed-out items in the trace are system library calls.
Items in black text are your code. Find the top-most item that is your code ( -
[TouchDrawView touchesBegan:withEvent:] ) and double-click it.
Figure 21.10 Stack trace
The source code for this implementation will replace the table of Line instances ( Fig-
ure 21.11 ) . The percentages you see are the amount of memory these method calls allocate
compared to the other calls in this method. For example, the Line instance makes up
about 47 percent of the memory allocated by touchesBegan:withEvent: .