. The compression tester is generally included in the list
  of necessary tools required for satisfactory automotive
  tuning due to the simple fact that a compression test
  will uncover many engine mechanical problems that cause
  rough running or poor performance.
. As cylinder compression test results are invaluable
  indicators of internal engine condition, most
  professional mechanics automatically check an engine's
  compression as the first step in a comprehensive tune-
  up. Obviously, it is useless to try and tune an engine
  with extremely low or erratic compression readings,
  since the remainder of the engine tuning work would be
  invalid.
. Included:
  . Compression tester.
  . Side-release valve.
  . Quick-release connector
  . Push-in rigid shaft with universal nisei cone
  . Flexible hose with 14/18 mm adaptor
  . Extension adaptor (for use with 5 to reach awkwardly
    placed or deep set plug ports)
  . Valve repair tool (for removing or tightening the
    valve built inside 3)