Just done a quick whizz through the site to patch up all mentions of Blumenfeld’s advice (which was passed on by Kotov and Webb in their best known books).  The advice is:

Blumenfeld’s rule:

“It often happens that a player carries out a deep and complicated calculation, but fails to spot something elementary right at the first move. In order to avoid such gross blunders, the Soviet master B. Blumenfeld made this recommendation:-
When you have finished your calculations, write down the move you have decided upon on the score sheet. Then examine the position for a short time ‘through the eyes of a patzer’. Ask whether you have left a mate in one on, or left a piece or a pawn to be taken. Only when you have convinced yourself that there is no immediate catastrophe for you should you make the planned move.“

— KOTOV
However, in the last FIDE revision of the rules, this practice is now considered note-taking, and is forbidden.  I don’t know how many players are complaining about it, nor how many controllers coming down on it (after all, this is a habit of some years’ standing for many players)… but it is illegal.  So what can we do instead?
Well, the idea is, to take a fresh look.  As long as you can make that last-minute check without the aid of props, you should do so.  Ways of producing a physical prompt or routine that don’t require pen and paper include:

• shut your eyes for a second or two
• walk around your chair
• look at the board next to you then look back
• go and stand behind your opponent and see how it looks from their side
• slap yourself firmly (it works for TVs, right?)
• visit your private toilet facility

I wish everyone a happy and blunder-free New Year, although yesterday I managed to get the order of moves reversed, with dire consequences… Physician, heal thyself!

P.S.

Contemporaneous comments from DrDave:

“You’ve all seen people do this. I’ve also seen people do it badly. The idea is to snap yourself out of the trance of analysis and take a fresh look. there are two basic ways of mishandling the method:

  I have seen players write down a losing move while nodding and smirking, look over the board again still nodding, and then play the move. Useless – just going through the motions. I guess they were just revising their latest thoughts on the position. You must jump! snap! start! your thinking again, to see if you have overlooked anything at the start of your thinking. You are not checking conclusions – you are checking assumptions. [If they had genuinely re-started their thinking there would have been a change in body language – not a smooth progression from choosing to writing to blundering, nodding all the while.]

 The second useless way of implementing Blumenfeld’s rule is to carry on thinking about the position. You see players with two, three, maybe four moves written down and crossed out over the course of fifteen minutes. This is hopeless indecision. You write the move down once you have decided on it. You then check it in case it is a blunder – not to see if you prefer another move. If there is nothing obvious tactically wrong with it, you must play it or you will run out of time. If you use the time to think about other moves you are not only wasting time, you are not even safeguarding yourself against blunders!”