Points
Points turns up in 3 fields: heat treating, powder coating, paper optics. Here is what it means to the people in each one.
Points in heat treating
Shop shorthand for Rockwell numbers, as in a part running two points high on hardness.
Floor unit for hardness differences: two points soft means two HRC numbers under the minimum. Heat treaters talk tempering adjustments in points, since a given change in temper temperature moves a given steel by a fairly predictable number of them. In steel grades, points also means hundredths of a percent carbon, so a 40-point steel has 0.40 percent carbon.
"They're two points over the print, retemper 50 degrees hotter and check again."
Points in powder coating
The titration reading for a washer bath, given in milliliters of titrant and used to judge bath strength.
Bath strength is checked by titrating a standard sample, often 10 milliliters, with a reagent until a color change; the milliliters used are called points. Cleaners, phosphates and acid stages each have a target range on the supplier's control sheet, and operators dose chemicals to stay in it. Free acid, total acid and their ratio are the key points for phosphate baths.
"Cleaner's at 6 points, sheet says 8 to 10, so add a drum before the next rack goes in."
Points in paper optics
Mill shorthand for units of brightness, opacity or whiteness on their percentage or index scales.
On the floor, a change of one unit of brightness or opacity is a point, so a sheet that goes from 92 to 90 brightness has lost two points. The word hides big cost differences: a point of brightness near 90 is far more expensive to gain in bleaching than a point near 80, and a point of opacity on a lightweight sheet can take a large filler increase. Points are always absolute units, never percent change.
"We gave up two points of opacity when they dropped the basis weight, and nobody told the printer."