Excel "$" , " " , "符號的意義

$是绝对引用的意思。比如你公式中使用A1，那么你使用拖动填充公式的时候，如果往下填充，下一条公式会自动变成A2，如果往右，会自动变成B1。如果你公式中使用$A$1，那么拖动填充的时候这个引用就不会变化。A$1这样是行不会变化，$A1是列不会变化。




Excel的進階應用，牢記「””」及「&」，文字串接免函數
http://www.techbang.com/posts/13027-excel-in-mind

Tapping screw

Below is a list of common tapping screw user’s complaints to screw suppliers:
 1. The screws strip out.
2. The screws will not seat in the application.
3. The screw break during installation.
4. The screw cause excessive driver bit usage.

Many times a thorough review of the screws reveals that they conform to all of their applicable requirements. The only logical conclusion to reach then is that the user is somehow unintentionally using the tapping screws inappropriately. After the screw supplier determines his screws are not the root cause of the user’s assembly problem he must work with the user to help determine what the root cause of the problem is. One of the most common assembly mistakes made by tapping screw users is inappropriate hole size selection. Extensive tapping screw hole size guidance is given in Appendix B of the American Society of American Engineers standard for tapping screws, ASME B18.6.4. This document contains recommended hole sizes for the use of all of the standard types of inch tapping screws from #2 through 3/8 inch in a variety of materials having a range of thicknesses from 0.018 through 0.500 inches. I will not reproduce the entire Appendix B in this article but I will provide excerpts to illustrate what information it does contain:

Laser Cutting Basics

With very little set up time, no tooling and the advent of CAD to CAM production, lasers are often utilized in prototyping and production parts. Well suited for intricate details and irregular contours, additional economies can be obtained through the nesting of parts when laser cutting.

Press Brake forming Basics

Press brake forming is the process of forming sheet metal along a straight axis using punch and die sets.  Typical punch and die combinations include “V” shapes, “U” shapes and in some cases channel shapes.

Sheet Metal Design Hand Book

http://www.qualitytool.com/resources/Design-Handbook-Rev3.pdf

*Footprint Graphics* or *Land Patterns*?

each CAD system developer picked their own names for what you are referring to; footprints, geometries, land patterns, cells, etc. but moving forward into the future we (the IPC) have found it useful to refer to them as "land patterns" and use the name "footprint" in a different way. You can think of a footprint as what you would see if you picked up a component and pushed it into sand or clay, the imprint it leaves would be its footprint, which is its actual physical size. The land pattern on the other hand describes the size of the pads needed to solder the leads to the board, which have wildly differing dimensions depending on what you are trying to do (wave soldering, reflow, high-density, etc.). So for a given part it will have one footprint but maybe several land patterns.
 
And, for the record, even though many of us are trying to use standard terminology, MANY are NOT, so you will still hear people talk about footprints as the pattern you see on a circuit board, probably forever!
 

Electrical discharge machining