"Whaddaya want? I'm old!" On top of that I had a lazy eye which wasn't treated, so while useful for general vision and depth perception, doesn't focus well enough to read with, regardless of glasses, only large type helps. So I'm a one good eye old guy. On top of that I have floaters in the good eye, and a cataract slowly creeping in. Why couldn't both of these things have happened in the bad eye where they'd have been no trouble at all?
But be of good heart. You didn't have a senior moment. They don't start until after 40. What you did was to make a perfectly normal transposition error, probably because you were typing quickly. My mother, who worked for the RAF during WW2 on human computers called Comptometers told me they were common entry errors so results were compared and if the difference of the two results of the same set of figures (everything had to be done redundantly like that) was 9 or a multiple of it when one was subtracted from the other, it was a guarantee of a transposition error, just like yours. Then they had to sit down, and one girl would read out the numbers going into the calculation while the other girl checked the two print outs or tabulations as they were called, comparing figures on both. Once they'd found the error, or errors, they knew which tabulation was correct. If both had screwed up, things got messier.
Just to make the whole thing worse, the machines were entirely manual which meant the numbers had to be punched in with both hands for amounts over 4 figures, like chords on the piano, all at once and using a fair amount of force leading to early onset arthritis of the hands. I can't remember my mother having normal knuckles, they were always bumpy, larger than the rest of her finger. Nevertheless she, and tens if not hundreds of thousands like her helped Britain survive and ultimately with US and Soviet allies win the war.
Dad was in the USAAC (US Army Air Corps) on light bombers, the Douglas DB7 which he called a Havoc but the Brits called a Boston. They married in '44 and I came along in '46 after they'd both come to my Dad's home city of Baltimore, where I was born and grew up.
Sorry but that was a little story about computers before computers. There is competition and controversy between the Brits and US over who built the first all electric programmable computer. The Brits built Colossus, and MIT built ENIAC. Colossus was used to break German codes as well as to do calculations on Bomb damage and a host of other things, ENIAC did many of the calculations or confirmations of calculations on the Atom Bomb. I don't know which, if either, used punched paper tape for programming.
So you're not having a senior moment, but a mild mistiming of your typing. When I'm having a senior moment I tell everybody that my Hard Drive is full and search times are really slow. The information always comes to me, usually before I've finished the letter or e-mail, but sometimes it's at 2AM when I take my night-time stroll to the loo, or the next morning. It rarely takes more than 24 hours, but I worry about that as a possibility.
Rob, mired in trivia from an early age.