Simple code, so I have no idea why it does not function.

```
ClrDraw
GridOff
AxesOff
CoordOff
0->Xmin
1->∆X
0->Ymin
1->∆Y
30->X
40->Y
Lbl 01
disp X
Line(X,Y,X,Y+20
disp X
Line(X,Y,X+15,Y
Line(X,Y+20,X+15,Y+20
Line(X+15,Y,X+15,Y+20
```

Outputs 30, then 0. What's happening during "Line(X,Y,X,Y+20" that is overwriting my X and Y variables?