请教木工角尺的问题

严丝合缝

太有意思了， 我是发现我的尺上有这几个字，于是就到google上搜了一下，结果居然又搜回来了，哈哈！

经过不屑的努力，找到了，英文的，看不懂，大概的意思明白了，是盖房子的时候用到的。
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有短视频但是一直也没出来
. f" m; a: \/ W  M3 w7 A' Nhttp://www.diynetwork.com/videos/swanson-speed-square/33081.html


; Z4 ~- _$ f$ A3 K! r3 K1 E+ ]在swanson公司的网站上有一点点关于这个尺的视频
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6 h5 W" \8 J5 N+ q) n4 Y. jUsing the Swanson Speed Square for Plumb and Seat Cuts
, h2 t" f$ E) m) i0 BThe speed square has a couple advantages over a normal steel framing square for marking and cutting rafters. Because of the pivot point at the corner of the square, you only need to line up one number rather than two. For example, to make a plumb cut on a rafter for a 6 in 12 roof, you just put the pivot at the corner of the rafter and line up the 6. Here is how it looks for a common rafter:
A second advantage is that the diamond hole in the square can be used to easily mark off seat cuts. The seat cut is where the rafter sits on the top plate. To do this, just line up the diamond with the plumb line you have just drawn and move the square towards the board until the pivot rests against the edge of the rafter. Becasue the distance from the diamond to the pivot is 3 1/2 inches (the same as the width of the top plate) the cut line will be 3 1/2 inches long and will be at a right angle to the plumb line. If this doesn't make sense in words, take a look at a picture or two. Line it up like this:
Then remove the area here:
Of course, the speed square is an old design. Where I am, the building code increasingly calls for the use of 2x6 framing instead of 2x4. This means that the diamond does not work anymore. But with a file and a black sharpie, you can modify your speed square to make seat cuts for 2x6 framing as well. To make aligning with a plumb line easy, I scribed a line entirely across the square. It looks like this now: