My object is the STAEDTLER® Mars® technico 780 C lead holder. I have 4 of them. One I've had since 1996, and the rest I've acquired later. In each I keep a different weight of lead: 6H, 4H, 2H and HB.

Affordances are subtle yet clear. The knurled end gives a tactile indication of where to best hold the lead holder; the clip keeps it secure in my pocket protector (ha, ha). As we expect, the end serves as a push-button to advance the lead. More unusually, it also serves as a sharpener, a possibility subtly suggested by its size (the same as the lead) and clarified by a diagram on the Staedtler website.

When the end is depressed, the lead advances. One potentially problematic aspect of the design is that unlike most lead holders, the lead does not advance incrementally. Instead, the push-button opens the jaws at the end that grip the lead, allowing the lead to potentially fall out of the pencil (an expensive error, at 2 bucks a lead). Once learned, it becomes natural to guard against this with your other hand when advancing a lead, and the infinite adjustability allows the lead to be sharpened to both a sharp and rounded tip, but perhaps a physical constraint could be introduced that prevents the lead from falling out completely.

There's no way to automatically differentiate between the different weights of lead, as the only available colour is blue. I've added an ugly label made of masking tape to each, which provides crude visible feedback, but it's an ugly solution at best.

Incidentally, the lead holder is yet another victim of the inexorable advance of digital technology. My supplier tells me that Staedtler will stop producing all drafting products in 2007. Another dinosaur, like film, which Kodak will stop producing in 2007. Perhaps the lead-holder (and the associated skill of hand-drafting) will experience a vinyl-like renaissance. In the meantime, I'll hold on to mine, beautifully constructed reminders and remainders of another age.