(Pa) The SI unit of pressure.
Definition: 1 Pascal is equal to 1 N/m² = 1 J/m³ = 1 kg x m^-1x s^-2
1 kPa = 0.145 lbf/in².
Air pressure is measured in hectoPascal (hPa), with 1 hPa = 1 millibar.
The unit is named for Blaise Pascal (1623-1662), French philosopher and mathematician.

(dB) A customary logarithmic measure most commonly used (in various ways) for measuring sound. Decibel is a way to express the ratio of two sound intensities: dB=10log10I1/I2 being I1 the reference. If one sound is 1 bel (10 decibel) 'louder' than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibel corresponds to an increase of 10 x 10 or 100 times in intensity.
The intensity of ultrasound is measured in db/cm and decreases during the propagation.
For sound pressure (the pressure exerted by the sound waves) 0 decibel equals 20 micropascal (µPa), and for ultrasonic power 0 decibel sometimes equals 1 picowatt.
See also Phon, Pascal, Logarithms, Proportionality Constant, Watt, Diagnostic Imaging.