# The first straight edge **URL:** \ **Category:** Factual Questions\ **Created:** [April 28, 2010, 8:54pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666 "2010-04-28T20:54:50Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![kornbln](https://avatars.discourse-cdn.com/v4/letter/k/838e76/32.png) [@kornbln](https://boards.straightdope.com/u/kornbln)\ **Post date:** [April 28, 2010, 8:54pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/1 "2010-04-28T20:54:50Z")
This question may have already been posed here, but I couldn’t find anything using the search. Google wasn’t much help, either. Anyways, my question is about straight edges. Today we have rulers, levels, and all sorts of instruments to draw and measure straight lines with. Well, how was the very first one made? How did they know it was straight? What did they measure it against? You don’t find many straight lines in nature, do you? I suppose one way to measure would be by stretching out a piece of string or hair, or water in a bucket. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [April 28, 2010, 9:02pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/2 "2010-04-28T21:02:18Z")
Would not the first straight edge have been a plumb bob? Because gravity points straight down. From that you can cut a straight piece of stone or wood. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [April 28, 2010, 9:03pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/3 "2010-04-28T21:03:15Z")
Another way is to take three plates of something rigid but machineable, make them as flat as you can by eye, coat them with blacking or something, and rub two of them together. The blacking will rub off the high spots, so grind down the visible high spots and repeat with another pairing. If you used only two plates you would end up with one convex and one concave, but with three, alternating between AB, BC and CA, they will all end up dead flat. Now you have something to check your straight edges against. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [April 28, 2010, 9:11pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/4 "2010-04-28T21:11:57Z")
Fold a hide in half; the fold is a straight line. ---
**Author:** ![magellan01](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@magellan01](https://boards.straightdope.com/u/magellan01)\ **Post date:** [April 28, 2010, 9:12pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/5 "2010-04-28T21:12:24Z")
A splintered tree? ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 28, 2010, 9:21pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/6 "2010-04-28T21:21:35Z")
> [@Fear\_Itself](#): > > Fold a hide in half; the fold is a straight line. Outstanding! 🙂 ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [April 28, 2010, 9:50pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/7 "2010-04-28T21:50:54Z")
> [@Quartz](#): > > Would not the first straight edge have been a plumb bob? Because gravity points straight down. From that you can cut a straight piece of stone or wood. That’s what I always imagined was used. Hang a weight on the end of a long wire/string and than line will be flat. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [April 28, 2010, 10:54pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/8 "2010-04-28T22:54:10Z")
> [@Quartz](#): > > Would not the first straight edge have been a plumb bob? Because gravity points straight down. From that you can cut a straight piece of stone or wood. You could also just pound two stakes in the ground and stretch a string taut between them. Since both ends are fixed, it would be easier to use as a guide for making a ruler. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [April 28, 2010, 11:05pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/9 "2010-04-28T23:05:58Z")
Minor Threat. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [April 28, 2010, 11:14pm UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/10 "2010-04-28T23:14:41Z")
A piece of gut, perhaps the small intestine of an animal, soaked in water, then twisted and stretched is the first type of cord made. A line of that cord, stretched between any two rigid objects, or by a weight suspended gives you straight, or vertical. When you have your two rocks rubbed mutually flat, you stretch a hide across one, press the other on top, let it dry, and you have a flat hide. Then you can rub mud on your cord, stretch it out, and twang it against the flat rock, and you have drawn a straight line between arbitrary points. The same cord can give you arcs as well, although accuracy depends on the sharpness of your compass points, and how easily your cord slides around your fulcrum. You have now the entire set of tools needed to do classic Greek geometry. Shouldn’t take you more than ten or twelve thousand years. Tris ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [April 29, 2010, 1:05am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/11 "2010-04-29T01:05:55Z")
I knew this bookmark would come in handy some day: [Making accurate straight-edges from scratch.](http://home.comcast.net/~jaswensen/machines/straight_edge/straight_edge.html) ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [April 29, 2010, 1:42am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/12 "2010-04-29T01:42:20Z")
> [@Fear\_Itself](#): > > Fold a hide in half; the fold is a straight line. Only if you fold it on a very flat surface. And getting such a surface is as hard as getting a straight line, maybe harder. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [April 29, 2010, 1:46am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/13 "2010-04-29T01:46:24Z")
> [@Malacandra](#): > > … … … Now you have something to check your straight edges against. If all you want is “something to check your straight edges against”, you don’t need any tools at all. Just put one end of the straightedge close to your eye, and the other end far away. Holding it in this position will magnify any imperfections and make them very easy to find. Try it! ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [April 29, 2010, 2:18am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/14 "2010-04-29T02:18:03Z")
> [@Keeve](#): > > Only if you fold it on a very flat surface. And getting such a surface is as hard as getting a straight line, maybe harder. That’s not true; I can fold a straight line without any surface at all. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [April 29, 2010, 3:05am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/15 "2010-04-29T03:05:20Z")
> [@Keeve](#): > > If all you want is “something to check your straight edges against”, you don’t need any tools at all. Just put one end of the straightedge close to your eye, and the other end far away. Holding it in this position will magnify any imperfections and make them very easy to find. Try it! Yes, the Mk 1 Eyeball is a valuable instrument when used properly, but will it tell a straight edge from a slight curve? ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [April 29, 2010, 4:47am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/16 "2010-04-29T04:47:59Z")
> [@Fear\_Itself](#): > > That’s not true; I can fold a straight line without any surface at all. What makes you think your folds are really straight? It’s definitely not guaranteed. (for kicks, I just tried folding two sheets of paper longways and comparing the folded edges. they definitely weren’t straight – there was about 1mm of cumulative error between the two of them over the course of 11 inches) ---
**Author:** ![magellan01](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@magellan01](https://boards.straightdope.com/u/magellan01)\ **Post date:** [April 29, 2010, 6:33am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/17 "2010-04-29T06:33:58Z")
> [@ntucker](#): > > What makes you think your folds are really straight? It’s definitely not guaranteed. > > (for kicks, I just tried folding two sheets of paper longways and comparing the folded edges. they definitely weren’t straight – there was about 1mm of cumulative error between the two of them over the course of 11 inches) Hides will be even harder, as there is less uniformity over the surface area. ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [April 29, 2010, 6:37am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/18 "2010-04-29T06:37:56Z")
> [@magellan01](#): > > Hides will be even harder, as there is less uniformity over the surface area. Yes, and in my experience, the thicker the piece of material you’re trying to fold, the more likely it is to curve as you crease it. ---
**Author:** ![Tim\_R.Mortiss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim_r.mortiss/32/142_2.png) [@Tim\_R.Mortiss](https://boards.straightdope.com/u/Tim_R.Mortiss)\ **Post date:** [April 29, 2010, 6:41am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/19 "2010-04-29T06:41:49Z")
> [@Malacandra](#): > > Another way is to take three plates of something rigid but machineable, make them as flat as you can by eye, coat them with blacking or something, and rub two of them together. The blacking will rub off the high spots, so grind down the visible high spots and repeat with another pairing. If you used only two plates you would end up with one convex and one concave, but with three, alternating between AB, BC and CA, they will all end up dead flat. Now you have something to check your straight edges against. This method is still commonly used in the machining world. But two surfaces are plenty, if you slide them around enough to avoid the concave/convex issue. And they use a compound called “blueing” not “blacking”…TRM ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [April 29, 2010, 7:17am UTC](https://boards.straightdope.com/t/the-first-straight-edge/537666/20 "2010-04-29T07:17:43Z")
snapping a chalk line creates a straight line and pulling a string tight in a bow saw configuration creates a straight edge. You could turn wood in a homemade lathe to form rods of fairly precise diameters using a gouge mounted in a fixed caliper. A roughly constructed wood plane would cut a pretty good straight edge. It may be a function of creating a better wood plane which would then cut a better straight edge. [Next page](https://boards.straightdope.com/t/the-first-straight-edge/537666.md?page=2)