Drawing electronic (digital) timing diagrams

Hi,

I want to use OmniGraffle to draw timing diagrams for electronic  
signals such as the (ASCII art :-) diagram below:

	|     _________________    _______________
	|    /                 \  /
	|   /                   \/
	+---                     ----------------------
	|   \                   /
	|    \_________________/
	|

To make drawing a little simpler I want to create stencils for a  
number of basic shapes, such as the first part above where the signal  
can both be high and low and the second part where a signal is high.   
The shapes themselves are to resize horizontally, but the slopes of  
the edges should stay constant.  Anyone an idea how to achieve that?   
Thanks in advance.

With kind regards,
Hans
--
Hans Zuidam
De Koppele 136, 5632 LD Eindhoven, The Netherlands
Tel. +31 40 2481546, Mob. +31 6 42345456
[email protected]