# Where should protected white spaces be used for numbers?

Protected whitespaces are used to prevent linebreaks in certain positions. For example:

I have watched a movie which consisted of exactly 1.2
million images.


is much worse to read than

I have watched a movie which consisted of exactly
1.2 million images.


so one uses 1.2~million or 1.2~million~images.

Now my question is if there is a good rule when to apply the protected white space.

For example, would should I use protected white space in the following situations? Should I use different approaches?

(1) This leads to a runtime of almost 2 minutes with our hardware.
(2) ... shows the output when using a stride of 37.
(3) a stride between 37 and 47 is sufficient.

• One rule I know is that there should usually be a protected whitespace between numbers and units (case (1)). Most of the time, I use siunitx in those cases. But what do I do when I want the unit spelled out? Should I still use siunitx? – Martin Thoma Sep 18 '15 at 14:42
• siunitx doesn't use ~ but \, (which is also non breakable). Where do you want to avoid breaking spaces? Another instance is Example 2, the whole expression is a name, which just happens to have an space character inside the name (in the same way as it has an m and a p, for instance), there you can indicate that the space is part of the name by using Example~2. – Manuel Sep 18 '15 at 14:46
• @Manuel I don't understand what you mean by "Where do you want to avoid breaking spaces?". I am asking for best practices when to use breaking spaces. I was only aware of ~, so another question is when to use \,. – Martin Thoma Sep 18 '15 at 15:06
• Not wanting to broaden the scope here too much, but here's another related thing I've always wondered about: in cases such as Example~2, should hyphenation of the word "Example" be inhibited? And if so, what is the recommended way to go about this? – Paul Gessler Sep 18 '15 at 15:08
• The first should have no number at all: almost two minutes (because “almost” is not mathematically accurate). I'd type a stride of~$37$ and a stride between $37$~and~$47$ is sufficient. But there's no hard and fast rule. Use ties generously: it's easier to remove them than to put them in after the fact. – egreg Sep 18 '15 at 16:18