The block library nobody maintains

26 August, the CAD server

The pattern room at Karnaphuli has been running for eleven years, and all its work lives in one folder tree. Somebody finally counted it.

38.2% of the files are named to settle an argument about which one is current, and that naming habit is the argument, not the answer. 15.7% of the library has been opened in a year. And there are 3.6 copies of every block, which is the number that costs money.

A block is a pattern kept because it will be used again — a men's chino front, a two-piece sleeve, a shirt body that fits this buyer. It is the most valuable thing a pattern room owns, and at Karnaphuli it exists 3.6 times over with no way to tell the copies apart.

Derivation is a copy, and a copy has no memory

On 14 March the men's chino front block was corrected: the fly curve moved 0.6 cm, because a fit comment on a different style had shown it pulling at the top of the zip. A pattern maker made the change, saved it, and was right to.

Eleven styles had been derived from that block between January and March. Every one of them carries the old curve. Nobody knows the eleven exist, because deriving a style from a block in this system means opening the block and saving it under a new name. The new file has no idea where it came from, and the block has no idea what came from it.

That is the whole defect, and it is not a discipline problem. A derivation that is a copy cannot be corrected, because nothing knows what to correct.

Two of the eleven were already in production on 14 March. That is a decision somebody would want to take deliberately, and never got the chance to.

The question that measures a library

There is one audit question. It needs no software, and the answer is a number in minutes:

How long does it take to answer which styles use this block?

At Karnaphuli it was measured. A pattern-room supervisor opened files, compared geometry and read notes for 3 hours and 40 minutes to answer it for one block. He was not slow. He was doing the only thing the library allows.

Recording the answer at the moment of derivation — a block identifier and a version, typed into the new file — takes about 20 seconds. The two numbers are the same fact from either end:

220 minutes to reconstruct     = 13,200 seconds
20 seconds to have recorded it
660 times

Recording it for all 611 styles would have cost 3.4 hours of typing, spread across eleven years.

The bill for one wrong reuse

CH-517, a women's chino, was derived on 2 April from a copy of the front block that predated the March correction. Nothing in the file said so.

It reached the pre-production sample. The sample was rejected on the fly, correctly, and the pattern was re-cut. The material cost was two samples, USD 96. The calendar cost was nine days, and the nine days came out of the end of the order. So 1,400 pairs went by air at USD 2.85 a pair more than the sea rate.

two samples                       USD    96.00
1,400 pairs of air freight        USD 3,990.00
                                  USD 4,086.00

USD 4,086 to reuse the wrong copy of a pattern the factory already owned and had already corrected.

The minimum record

A block does not need a system. It needs seven fields, and a spreadsheet holds all seven.

1. An identifier that never changes, even when the geometry does. The identifier names the block; the version names the state of it.
2. A name a human would search for — the garment, the fit, the buyer if the block is buyer-specific.
3. A definition: which body and which fit this block is for, in one sentence. This is the field that stops a men's chino front being used on a woman's chino because the outline looked close enough.
4. A version and a date.
5. A steward — one named person who approves a change to it.
6. What changed, in one line, at each version.
7. What derives from it — the style codes, added at derivation.

Fields 1 to 6 are what most pattern rooms already write somewhere. Field 7 is the one that is always missing, and the only one that would have caught the March correction, because it is the only field that points forwards.