First, input either the engine size (in cc) OR the bore/stroke.
Then complete the other fields, or press the 'Default' button
to approximate any required data items according to your engine size.
Then press 'C/R' to get a calculation of the compression ratio. Once this is done
the required combustion chamber volume can be calculated by changing the
compression ratio to the desired value and pressing the 'Chamber' button.
The amount to skim off the head to achieve this C/R can be
measured or calculated.
Pressing 'Default' at any time will restore the default values according to engine size, otherwise most values may be modified and either 'C/R' or 'Chamber' calculations repeated with the new values.
Enjoy!