Volks,
  
In doing the measuring for calculating the compression ratio for your 
engine, one might wonder to the degree of accuraccy needed in making 
the various measurements.

See Bob Hoovers' sermon on "Deck Height and Comp. Ratio" for the 
details on what needs to be measured.  I ran a sensitivity test on 
the parameters I needed to measure to determine the compression ratio 
for my engine.  The parameters I measured were:  Deck Height, Stroke, 
and Chamber Volume.

How accurate do I need to make these measurement in order to get a 
"good" estimate of compression ratio (here-to-fore referred to as 
CR).  The sensitivity test was perfomed by varying one of the above 
parameters (while holding the others constant) and observing the 
change in the calculated CR.

============================================
Change in Deck Height by 0.1 mm:

A   Stroke: 69 mm
      Chamber Vol: 49.2 cc
      Deck Height: 1.7 mm
      CR: 7.72

B   Stroke: 69 mm
      Chamber Vol: 49.2 cc
      Deck Height: 1.8 mm
      CR: 7.65

Conclusion:  prolly should measure deck height out to the nearest 
0.01 mm

==============================================

Change in Compression Chamber Volume by 1 cc:

A   Stroke: 69 mm
      Chamber Vol: 49 cc
      Deck Height: 1.7 mm
      CR: 7.74

B   Stroke: 69 mm
      Chamber Vol: 50 cc
      Deck Height: 1.7 mm
      CR: 7.63

Conclusion:  prolly should determine out to the nearest 0.1  cc

==============================================

Change in Stroke  by 0.1 mm:

A   Stroke: 69 mm
      Chamber Vol: 49.2 cc
      Deck Height: 1.7 mm
      CR: 7.72

B   Stroke: 69.1 mm
      Chamber Vol: 49.2 cc
      Deck Height: 1.7 mm
      CR: 7.73

Conclusion:  prolly should measure deck height out to the nearest 0.5 
to 1 mm

==============================================
Thought this might help,
christian f krahforst 
UMass/Boston
7039ckrah@umbsky.cc.umb.edu