Is it possible to add plus minus symbol in math field?

[Kivi_Kn]

Is there a way to get the plus minus sign ± into math field? I couldn't find it from the symbols list so I guess the only way of getting it into the document is to copy+paste. However, Mathcad doesn't allow me to paste it into math-field, only to text fields...

[ttokoro]

Usually, you can't. If you can use 2-byte code, it is possible. 

[Werner_E]

There is no +- operator in Mathcad, but you could define your own function and use it like this

In Mathcad (but not in Prime) you can even let it look like this

In Prime you only can write it that way

Remark: Only type round parentheses.
The square brackets are shown automatically when you use Mathcad, Prime will show round parentheses only.