code: private void movePos(float deltaY) {
          // has reached the top
          if ((deltaY < 0 && mPtrIndicator.isInStartPosition())) {
              if (DEBUG) {
                  PtrCLog.e(LOG_TAG, String.format("has reached the top"));
              }
              return;
          }
  
          int to = mPtrIndicator.getCurrentPosY() + (int) deltaY;
  
          // over top
          if (mPtrIndicator.willOverTop(to)) {
              if (DEBUG) {
                  PtrCLog.e(LOG_TAG, String.format("over top"));
              }
              to = PtrIndicator.POS_START;
          }
  
          mPtrIndicator.setCurrentPos(to);
          int change = to - mPtrIndicator.getLastPosY();
          updatePos(change);
      }
docs: if deltaY > 0, move the content down
  
  @param deltaY