Superscript plus sign

Mostly in chemistry and physics, where it means positive charge. H⁺ is a hydrogen ion, NH₄⁺ ammonium, Ca²⁺ a calcium ion that has lost two electrons. The number comes before the sign: Ca²⁺, not Ca⁺². In physics, e⁺ is the positron and π⁺ a positive pion.

In mathematics it marks the positive side: x → 0⁺ means x approaches zero from above, and ℝ⁺ usually means the positive real numbers (some books include zero).

Typing a normal + and applying superscript in a word processor looks the same, but that is formatting, and it disappears whenever the text lands as plain text: in many chats and social posts, and always in a file name. ⁺ is its own character and keeps its raised shape in plain text, as long as the font has it. For formal documents, formatting is usually fine; for plain text, use ⁺.