The first number (dBu) is the signal strength, the second is a more interesting number that, although characterized as "S/N" or signal to noise ratio, does indicate more like "quality of reception" factor, and if it was simply S/N, should technically have a minus sign I would think.
For AM and SW, the second number does end up at 25, and I've never seen it higher than that.
On FM, things get interesting. I've seen signal strengths top out at 72dBu and for most stereo signals devoid of multipath, the "S/N" varies from 44-55. One exception was CBC radio 1 in Kingston... I was on Via Rail and it hit 75 on the dBu display and 75 on the "S/N".. Never got it to repeat that on subsequent Via travels to Ottawa. :-)
For strong multipath riddled signals, I've seen dBu's of 35-55 range and "S/N"s of 07-18 before they become tolerable... And yes, the more processed a station is, the lower the "S/N" can show... Interesting to observe...
That 60-70dBu by the way is quite strong, for any signal received.
DAB listener 12/2003-11/2011 (DAB Off-Air since 11/2011)
HD radio Listener since 06/2010