fifth valve is commonly tuned to a flat whole step, so that when used with the fourth valve, it gives an in-tune low B. The sixth valve is commonly tuned as a flat half step, allowing the F tuba to play low G as 1-4-5-6 and low G as 1-2-4-5-6. In CC tubas with five valves, the fifth valve may be tuned as a flat whole step or as a minor third depending on the instrument. Compensating valves Some tubas have a compensating system to allow accurate tuning when using several valves in combination, simplifying fingering and removing the need to constantly adjust slide positions. The most popular of the automatic compensation systems was invented by Blaikley (Bevan, 1874) and was patented by Boosey (later, Boosey and Hawkes, which also, later still, produced Besson instruments). The patent on the system limited its application outside of Britain, and to this day, tubas with compensating valves are primarily popular in the United Kingdom and countries of the former British Empire. The Blaikley design plumbs the instrument so that if the fourth valve is used, the air is sent back through a second set of branches in the first three valves to compensate for the combination of valves. This does have the disadvantage of making the instrument significantly more "stuffy" or resistant to air flow when compared to a non-compensating tuba. This is due to the need for the air to flow through the valves twice. It also makes the instrument heavier. But many prefer this approach to having additional valvesor to the manipulation of tuning slides while playingto achieve improved intonation within an ensemble. Most modern professional-grade euphoniums also now feature Blaikley-style compensating valves. Resonance and false tones Some tubas have a strong and useful resonance that is not in the well-known harmonic series. For example, most large B tubas have a strong resonance at low E (E1, 39 Hz), which is between the fundamental and the second harmonic (an octave higher than the fundamental). These alternative resonances are often known as false tones or privileged tones. Adding the six semitones provided by the three valves, these alternative resonances let the instrument play chromatically down to the fundamental of the open bugle (which is a 29 Hz B0). The addition of valves below that note can lower the instrument a further six semitones to a 20 Hz E0. Thus, even three-valved instruments