Hi There Everyone.

I hope you're all well.
I had a question,
I'm really lost - i need to create a first difference operator in stata, I've been struggling to understand how to do this.

My data looks like this:
observation Year quarter r bill rate pi
1 1950 1 0.51 11.53832 0.5
2 1950 2 0.51 11.53832 4.06
3 1950 3 0.55 11.56103 5.5
4 1950 4 0.623 11.60105 9.85
5 1951 1 0.693 11.61927 14
6 1951 2 0.75 11.60116 11.67
7 1951 3 0.803 11.5962 8
8 1951 4 0.913 11.59763 3.26
9 1952 1 0.907 11.64858 3.39
10 1952 2 1.013 11.67504 -2.93
11 1952 3 1.11 11.68812 -2.58
this is the regression i have to run Array

basically Δrt=rt​​​​​​ - rt-1​
Any help and guidance would be greatly appreciated please.