Compression testing apparatus

DETAILED DESCRIPTION What is claimed is: 1.
A Apparatus for testing the compression of an internal combustion engine including a first chamber, a second chamber, a first member movable inside the first chamber in order to compress gas within the first chamber during a first time period, a second member movable inside the second chamber in order to compress gas within the second chamber during a second time period, a starter motor for moving the first and second members during a starting period and an electrical system for supplying an electrical power signal to rotate the starter motor during the starting period, and apparatus comprising: converting means for generating a first group of discrete digital amplitude signals having values proportional to the amplitude of the electrical power signal at a plurality of discrete times during the first time period and for generating a second group of discrete digital amplitude signals having values proportional to the amplitude of the electrical power signal at a plurality of discrete times during the second time period; processing means for selecting from the first group of discrete digital amplitude signals a first representative signal for representing the compression of the first chamber, for selecting from the second group of discrete digital signals a second representative signal for representing the compression of the second chamber and for generating relative compression digital signal having a value depending on the relative values of the first and second representative signals; and display means for displaying the value of the relative compression digital signal.
2.
Apparatus, as claimed in claim 1, wherein the converting means comprises means for generating digital amplitude signals having values proportional to the current amplitude of the electrical power signal.
3.
Apparatus, as claimed in claim 1, wherein the converting means comprises means for generating digital amplitude signals having values proportional to the voltage amplitude of the electrical power signal