Punched cards (Was: 1" paper tape buy ?

[Philip Belben]

[cards for sorting with needles]

William Donzelli asserted:

> It is actually a trinary system - hole, no hole, or slot.
> Additionally, the edges could be multiple levels deep (generally two),
> so you could do multiple level sorts.

Are you sure about the "no hole"?  I query this for two reasons:

Firstly, the deck I have of blank ones has all the holes around the edge 
pre-punched.

Secondly, how would you sort?  If there are any cards at all in the deck 
with the hole filled, you can't sort in a single operation.  You have to 
drill down to the filled hole and split the deck; extract the 
filled-hole cards; and repeat until you've got to the end.

(To put it another way, you cannot detect any holes in cards sandwiched 
between two filled-hole cards without splitting the deck)

I like the idea of a second hole, further in.  This implements ternary 
rather nicely: the states are no slot, shallow slot, deep slot.  (Needle 
in outer hole leaves all cards with slots.  Needle in inner hole leaves 
only cards with deep slots).  A fourth state joining the two holes 
without taking the slot to the edge is possible but not recommended, 
because the cards don't come off the needle, they just hang at different 
heights, making them harder to handle.

Philip.