What is decibel ? i heard this is not absolute value like Volume

there is lots of knobs in cubase that measured in Db

and it’s rather hard to make any measurements when u don’t know what is Db

The decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity (usually measured in units of power or intensity).

A change in power by a factor of 10 is a 10 dB change in level. A change in power by a factor of two is approximately a 3 dB change. A change in voltage by a factor of 10 is equivalent to a change in power by a factor of 100 and is thus a 20 dB change. A change in voltage ratio by a factor of two is approximately a 6 dB change.

It is easier to grasp and compare 2- or 3-digit numbers than to compare up to 10 digits.

If it makes it any easier, just make a parallel comparison and use the decibel unit scale as you would a scale of 1 - 10 on a volume slider/knob.