def _val_in( val_0, magnitude ):
	"""
	Returns magnitude with the sign such that abs(val_0 + mag2) < abs(val_0) 
	If mag < 0, does the opposite.
	If abs(mag) > 1, may result in an overshoot.
	"""
	if val_0 < 0:
		pass
	elif val_0 > 0:
		magnitude = -magnitude
	else:
		# Because one cannot draw closer to 0 if one is already there:
		if magnitude > 0: magnitude = 0
		# And since we don't want d to be always negative:
		else: magnitude = -magnitude

	return magnitude