So, which ruler was right?

The caption says two rulers don't match up, so which one is right?

I don't know, but any ruler

I don't know, but any ruler is easy to check.  3.5mm = 1 foot, so 3.5cm = 10 feet and 7cm = 20 ft.  At this point, find a good reliable metric ruler and check it up.  If the scale ruler is good, it will line up 20ft at 7cm, 40ft at 14cm, and 80ft at 28cm.  And this is one case where I'm not happy unless it's accurate...+/- 1mm in 100 mm is pretty much out of tolerance for me.  The standard HAS to be accurate!!

Accuracy is every thing

particularly when scaling. Soft measurements are ok to estimate example; 25 mm = 1 inch however, when it comes to actual construction (25.7) should be 25.4 mm = inch that (.7) .4 makes all the difference.

I concur with Benny, if building a gradient or any measurement exceeding 6 inches near enough is NOT good enough.  

Ooops

My source says 25.4 mm to the inch.

You are correct!

I was having a Seniors moment too much information stored in my head, sometimes the retrieval system is not good enough or accurate enough. Just goes to show going the distance can lead you astray

That inch conversion leaads

That cm to inch conversion leads to all sorts of trouble, hence why I keep "3.5mm = 1 ft" handy.  You will always be guessing if you're using 2.54cm = 1in, 1 ft = 87.1ft.  Yech.  So pull out the metrics, and suddenly it's easy to convert!

I even converted an old cm stick to Ho once when I was a kid.  It didn't have the mm markings, so I added them.  It was crude, to say the least.

Which Ruler is right?

Okay, I hunted down my steel "General No. 1251 Model Railroad Reference Rule" and compared it to the other two. The transparent one matched it. The Rulers of the World Ruler is first noticably off at the 13 ft. point - before that it's within the line used to mark the distance. At it's 45' mark, it's at the other rulers 44' mark. Basically I wouldn't use this ruler for exact precision work - since it's only marked in feet (the steel one, which I remember being significantly more expensive is marked in quarter feet and has an inches breakdown at one end as well. This is more of a quick "whip it out to check something" type ruler. And if you are like me, who is astonished that all three of my HO scale rulers are actually in the same place right now, it might be a good one to acquire several of, just to keep one handy.

Metrics

Why on earth this otherwise great country keeps fuddling with such an archaic and cumbersome measuring system is beyond my understanding... only made worse when I read somewhere that Congress approved the metric system way back in the 19th century.

About accuracy, I have a high quality caliper. Every other measuring tool gets checked against it before purchase and if does not measure up gets back on the seller's shelf.

O scale is sooooo easy

1/4" to a foot.  1 inch is 4 feet.  A 40 foot boxcar in 10 inches long.............................I'm spoiled!!!

Peter

O scale is soooo easy

And one railroad is... more room than I have available.

I'll stick with HO and Z, thanks!