Industry/CAD Standard Question

So most of my drawings have multiple scaled viewports on one paperspace. I call out those scales. My predecessor did it different from me. So here's the question...

Do you use 1:1.5, .75:1, etc or do you use 2:3, 3:4, 2:5?

Whats your personal preference?

Are we talking metric scales?

Negative. They are inches. Basically the scale is 75% of actual. So do you write that as .75:1 or 3:4. I personally don't like having decimals in a ratio. I'm asking here to reach out to other engineers/manufacturers/smart CAD people.

Using decimal points like this can lead to reading errors.

.... I personally don't like having decimals in a ratio. .....

Conventionally, a scale is expressed as one unit on the paper drawing (hard copy) is equal to so many units (decimals or fractions) in real life.

Your personal preferences will lead to confusion in others. If you want clarity, stick to convention.

We are metric but a scale would be 1:1 1:2 1:4 not 0.75 sounds to me to be a odd scale, we can buy scale rulers here and 1:750 is a scale available but its metric.

.....Basically the scale is 75% of actual. So do you write that as .75:1 or 3:4......

I would write that as 1:1.333

Well no you wouldn't write it that way. From what you have told us 1 unit in paper space is equal to 75 units in model space so you have a 1:75 ratio so 1"=75". If you want to maintain that ratio for any scale then you would multiply your ratio by the scale. For example if you wanted a 1/2" scale then it would be 1/2"=42.5". But this is a stupid way of doing it. Remember the imperial system is not base 10 like the metric system, sure there's a decimal version of it but only super nerds use it and very few of them at that, it's base 12 so any scale you use needs to reflect that so if you want a scale close to 75% then 9"=12" which is 9/x=12 solve for x gives us x=9/12 simplify and you get 3/4 or .75 which is the same as 75%. Your scale, if you are using a measurement system that is base 12, would be 9"=12".

Disregard the paper units to drawing units. I am simply asking if you are notating the scale of the image would you write 3:4 or .75:1, or as Eldon said 1:1.333 repeating. They are the exact same scale just written different.

Then your ratio would written as 3:4. Ratios are always whole numbers just like fractions and they should be written in their simplest from meaning that neither side of the ratio can be divided by a whole number. Best thing you can remember about a ratio is that it's neither inches or metric. It's a unitless comparison between two things.

Scales are unitless, so it doesn't matter if you are working with imperial or metric units a scaled viewport magnifies, or reduces, a model by a specific factor. True, is that when working with imperial units certain scales are normally used and in metric units other scales are used, with some overlap. Different professions use different scales, a surveyor could use a scale 1:10000, but for for someone manufacturing parts for watches such a scale would be unthinkable.

But as has been said above, scales such as a:b are usually written in whole numbers not with decimals, and at the same time reduced to the lowest possible numbers, so a scale of 4:8 is written as 1:2. In your case the scale would be 3:4, as has been clearly said above.