5:5
Slang Report Formats (Five by Five; 5:5)
A report format commonly referred to as five by five is often used in media. The report format ostensibly consists of two digits, each ranging from 1 to 5, resulting in 25 possible combinations, with five by five being the best signal possible out of 25 combinations. As no reliable source has been found documenting this format, it may simply be Cold War-era slang, inappropriately mapping the radiotelegraph signal report numbers to radiotelephony signals.
Some radio users have inappropriately started using the Circuit Merit telephone line quality measurement. This format is unsuitable for radiotelegraph or radiotelephony use because it focuses on voice-to-noise ratios, for judging whether a particular telephone line is suitable for commercial (paying customer) use, and does not include separate reports for signal strength and voice quality.