Newer EFIS systems make such checks superfluous. Generally the left and right systems contain comparator circuitry and any difference in parameters between the systems will generate a warning on the screen. Some of the parameters and their triggering differences include Pitch – five deg. Roll – six deg. Heading – 12 deg. Localizer – half dot. Glideslope – three quarter dot. IAS – 5 knots and Altitude – 200 feet. Of course the balance ball may still be mechanical and require checking!