How to find the centerpoint on straight lines.

[kgg]

I finally got tired of doing calculations in my head when trying to find the centre of something. Since I was taught, trained and worked in the Imperial and US systems until Canada converted supposedly to the Metric system. Normally the Imperial system is my go to for everyday type measurements. 

So I finally broke down and bought a 12" centre finding ruler sometimes called a doubling ruler. 

The ruler:

i) Imperial measurements up to 12" or a you can get a larger 24" version

ii) Two scales. A measuring scale and a centre point scale

iii) Material: Tempered Stainless Steel

iv) Sold by US Tape Company (https://www.ustape.com/product/centerpoint-straight-edge-rulers/)

v) Made in China

vi) patent number: 5,251,382 which is for a tape measure not a ruler???? 

vii) Status: Expired - Lifetime

viii) Cost: I paid $18.90 CAD plus tax for total of $21.35 CAD ( $15.35 ) from Lee Valley

This is a very simple design. You just measure the item say 8 1/4" and find 8 1/4" on the bottom scale and that is the centerpoint location. 

Anyone with a laser or 3d printer could easily make one.

To bad they don't have a metric version for better accuracy.

kgg

 

[fredk]

I've been using a metric centre-finder ruler for several years

I don't  really bother with the actual measurement; I just get the ruler onto the line, get the same distance number on each side and voila, the centre be found

[toxo]

As Fred said Keith. This one is stuck down on the mat.

This one is just a ruler. Just move the piece so it reads the same both sides and mark the center.

[kgg]

@toxo and @fredk The more options the better. Like when I am doing a dog lead I use a 6' steel ruler. 

kgg

 

[GerryR]

For shorter lines, you can use a compass and swing an arc on both sides of the line from both ends with the compass set at a distance greater than half the line length. Connect the intersections of the two arcs on each side of your line, and you have a line perpendicular to the original line directly thru its center.  Helps if you don't have a ruler.  For longer lines, make a compass from a piece of string and a pencil or marker.