How to display field value in a text box

Is there a way to put a value of a field in a text box? For example i have a KPI which i am displaying, and a target i am displaying. I have a field to workout the difference, which i want to display. The thing is that i want a ‘+’ to be displayed before the number if it is more than 0, or a ‘-’ if it is less than 0. How can i put a value of a field in a text box so i can achieve this?

OR, how can i put a ‘-’ or ‘+’ before this kpi to display whether it is a negative or positive?

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you may use KPI and add Icon to show +, if it is higher than zero.
And show -, if it is below zero