If you open tins here's a must

So why is the Brabantia tin-opener so good? One reason is that significant forces are concentrated at the notched wheel (which drives the opener round the rim of the tin) and the disc blade (which is pressed into the tin end and does the cutting). On cheaper openers the spindles on which these two components rotate wear quickly and both wheel and blade become loose. When the play is so extensive it is almost impossible to squeeze the handles together sufficiently to drive the blade through the end of the tin.

The photo can't show how securely the notched wheel (on the right) is mounted but I can assure you the spindle diameter is twice that of cheaper openers. But the key to the design is the mounting of the blade (which has its own idling notched wheel to grip the other side of the rim of the tin). For one thing the spindle is mounted at an angle. Thus when the driven wheel and blade are squeezed together they operate optimally. Second, even when spindle and blade begin to wear, they are held in position by the curved spring which engages with the free end of the spindle.

I'm afraid it's all a bit wordy. The qualities are easier to understand when you see the Brabantia "in the metal". It only remains for me to add I am not in the pay of Brabantia. I simply like things that work, and this does.

Learn on the couch, not in the car

SATNAV - Part three No, I'm not in thrall to this technology and freely admit it has some way to go. But it's had an undeservedly bad press from people who've tried it for an afternoon, failed to realise its potential and - a particular bête noire - have written delightedly about their inability to penetrate its workings.

One accessory worth acquiring is the cable/transformer that allows you to plug the satnav in to your house supply and play around with it in the comfort of your own living room. You learn far more in this unstressed environment. When you try similar experimentation in the car it always seems too hot and your sweaty finger-tips skitter over the controls.

I think that's enough about satnav. To tell the truth I respond more viscerally to maps but satnav's proof I'm trying to be a child of our times.

TECHNO-ART Other than documentaries which are outside my scope I find TV rather barren of examples in which art fuses with technology. One exception was "Das Boot", the German multi-episode series about life in a WW2 submarine. Here men were surrounded by technology and threatened by it from above. Big batteries were big, too. But I'd appreciate an explanation about that greenish light emanating from small windows - apparently - on the side of the diesel engine cylinders.