Why should I use this instead of other software?

It runs in the browser. It is also completely free and delivers the same level of precision you would expect from equivalent desktop tools.

How do I calibrate the microphone?

There are two answers to this question:

• The first alternative is to use a pistonphone or sound calibrator that generates a 94 dB 1 kHz tone. Examples include Brüel & Kjær Type 4231, G.R.A.S. 42AB, iSEMcon SC-1, and lower-cost options such as the AZ 8930 calibrator.
• The second alternative is to use a reference microphone with a known sensitivity and enter that value in the calibration settings. An example is the miniDSP U-MIK2.

How precise are the frequency weightings?

The A-, C-, and Z-weighting responses are implemented to match the published reference curves for sound-level measurements by a 0.25 dB tolerance. For background on the weighting standards and their expected frequency response, see NTi Audio's frequency-weighting reference.