This is just a quick question about the convention used to write units. My assumption is that you wouldn't leave spaces between different units, but i could see this could lead to potential confusion. should i write: kms-1Mpc-1 or km s-1 Mpc-1 I guess it's normally clear from what you're talking about and i don't think there are any letters used for more than one unit. Just want to check the convention. I assume it is without spaces? EDIT: there is a case where letters are used more than one thing, ms-1 could be per micro-second or metres per second. Guess it'd be obvious in context though?