Wow! signal
On this scale, an empty space was left for strengths between 0 and 1 standard deviations higher than the background noise. The numbers 1 to 9 showed how many standard deviations above the background noise the signal strength was. If the strength of the signal was 10 or above it would be indicated by a letter: "A" corresponded to a strength of 10, "B" to 11, "C" to 12, and so on. The Wow! signal's highest measured value was "U" (a strength of 30), making it thirty standard deviations above background noise.John Kraus, the director of the observatory, gave a value of  in a 1994 summary written for Carl Sagan. However, Ehman in 1998 gave a value of . This is () above the hydrogen line value (with no red- or blue-shift) of . If due to blue-shift, it would mean the source was moving about  towards Earth. An explanation of the difference between Ehman's value and Kraus's can be found in Ehman's paper.