public void flush() {
            if (!mTracking) {
                return;
            }

            // save to file on sdcard
            try {
                boolean append = true;
                if (mNumFlushes == 0) {
                    append = false;
                }
                FileWriter writer = new FileWriter(mFile, append);

                writer.write(mBuilder.toString());
                mBuilder.delete(0, mBuilder.length());

                writer.flush();
                writer.close();

                mNumFlushes++;
            } catch (IOException e) {
                // do nothing
            }
        }
Return a scroll speed in pixels/millisecond. Always return a
positive number.

@param w Normalized position in scroll region (i.e. w \in [0,1]).
Small w typically means slow scrolling.
@param t Time (in milliseconds) since start of scroll (handy if you
want scroll acceleration).
@return Scroll speed at position w and time t in pixels/ms.
third_party/DragSortListView/src/com/mobeta/android/dslv/DragSortListView.java