The legal range is defined in an SAE standard or whatever authorities in your country copied from the SAE.
From memory the variance allowed is huge. Anything between 0.25Hz to 4Hz is allowed. But it is a long time since I read the actual standard.
The legal range is defined in an SAE standard or whatever authorities in your country copied from the SAE.
From memory the variance allowed is huge. Anything between 0.25Hz to 4Hz is allowed. But it is a long time since I read the actual standard.