Scale 1:25 or 1:75 why scale ruler first reading is 0.5m and 1m respectively ?

[zillah]

Dear folks

Yes I do understand scale ration 1:25 means 1 unit on a map equal to 25 units on a real and scale ration 1:75 means 1 unit on a map equal to 75 units on real

Question my Kent tri scale ruler showing first number for ratio 1:25 as 0.5 m (i.e 50 cm, 500 mm) while first reading for ratio 1:75 as 1 m (100 cm, 1000mm) ?

My confusion for the ratio 1:25 ruler has 25 small tiny line between 0 and next reading means 25 units right ?? if I multiply 25*25 = 625 why scale reads it as 500 mm or 0.5 m????

Same thing for the ratio 1:75 ruler has 20 small tiny lines between 0 and next reading means 20 units right ?? if I multiply 20*75 = 1500 why do I have 1000 mm or 1 m ????

Thanks

[Strange]

1 hour ago, zillah said:

Question my Kent tri scale ruler showing first number for ratio 1:25 as 0.5 m (i.e 50 cm, 500 mm) while first reading for ratio 1:75 as 1 m (100 cm, 1000mm) ?

Not sure what the question is. But the first number show will just be whatever is convenient for that scale (i.e. usably large and rounded to a sensible number).

1 hour ago, zillah said:

My confusion for the ratio 1:25 ruler has 25 small tiny line between 0 and next reading means 25 units right ?? if I multiply 25*25 = 625 why scale reads it as 500 mm or 0.5 m????

The units for each division would be 0.5m / 25 or 20mm.

[zillah]

Quote

The units for each division would be 0.5m / 25 or 20mm.

Thanks Strange

if each division would be 20 mm that means our ratio should be 1:20 not 1:25 right ??

[Strange]

The scale and the number of subdivisions are not necessarily related. 

[zillah]

>> The scale and the number of subdivisions are not necessarily related.  <<

I couldn't be convinced

[Strange]

Well, Geta. strip of paper make your own scale ruler where one centimetre equals one meter (in other words 1:100) and just draw the centimetre marks. Each mark corresponds to 1 metre and you can label them like that.

Now you can subdivide those centimetre marks to allow more precise measurement to be made. For example, you could put a half-centimetre (half-metre) mark between each one. It is still a 1:10 scale not a 1:2.

You could put 2 subdivision marks between each centimetre, so each is roughly one foot. It is still a 1:10 scale and not 1:3.

And so on.

Edited August 21, 2017 by Strange

[zillah]

Yes I can do that but I want to find out where is my confusion

1:25 showing 25 subdivisions (tiny lines) right ?

http://imgur.com/a/CmVFe

While for 1:75 showing 20 subdivisions (tiny lines) right ?
http://imgur.com/a/42AyT

[Strange]

In both cases, the subdivisions are chosen to be practical (close enough to allow accurate measurement but not so close that they can't be distinguished) and to correspond to a sensible subdivision (multiples of 5 or 10; dividing by multiples of three would be silly).

The fact that the 1:25 has 25 subdivisions is just a coincidence.

[tar]

Zillah,

I could be wrong, but I think your confusion is in trying to have both scales work on the same map.  They will not. because each scale is used uniquely to mark out only one map.  

Like the treasure map in Goonies, do you march out in kid paces or pirate paces.  A pirate will take less paces to travel a mile than a child.

Regards, TAR

[zillah]

Quote

I could be wrong, but I think your confusion is in trying to have both scales work on the same map.  They will not. because each scale is used uniquely to mark out only one map.  

tar this is not the case , i gave them as an example

[tar]

Zillah,

OK, figured it out.  My tri ruler is marked out in divisions per inch (10,20,30,40,50,60).   Your ruler is marked out in ratio to a meter.   The 1:25 took 1000mm and divided it by 25 to show the one meter mark at 13.33 millimeters.  The 1:75 scale takes a 1000mm and divides it by 75 and puts the 1 meter mark at 40 mm and the half meter mark at 20 mm.  Since an inch is about 25.4mm, the meter mark on the 1:25 scale should land around 1/2 inch (13.3mm) and the .5 meter mark on 1:75 to land a little to the right of 3/4 of an inch.

In terms of why the subdivisions from there are the way they are, listen to Strange.  

Regards, TAR 

[Strange]

23 minutes ago, tar said:

The 1:25 took 1000mm and divided it by 25 to show the one meter mark at 13.33 millimeters. 

What?

1 metre divided by 25 is 40mm.

25 minutes ago, tar said:

Since an inch is about 25.4mm, the meter mark on the 1:25 scale should land around 1/2 inch (13.3mm) and the .5 meter mark on 1:75 to land a little to the right of 3/4 of an inch.

Inches? Who cares!

[tar]

sorry I mixed my calculations, the 1:75 landed on the 13.3 mark

Inches only matter to people who don't think in mm.  I didn't know which mode Zillah is more comfortable in, but in any case, a mark on a ruler at 25.4 mm is going to be an inch from the 0 mark. So looking at his picture of his tri I lined up mine in front, to the same size by moving it in between my eye and my computer screen 'til the two were the same size (assuming that the stock unmarked tri is a standard size) and was able to thereby understand where an inch would land on his ruler, and it made the first mark on each scale understandable to me...so I thought the same understanding would resolve Zillah's confusion.

Edited August 21, 2017 by tar