*ROOT Version:* 6.18/00

*Platform:* Red Hat 8.5.0-16

*Compiler:* gcc version 8.5.0

Hello everyone,

I want to fit a histogram (see figure) with the crystal ball function following the code:

```
TF1 *fitFunction = new TF1("fitFunction", "crystalball", 84, 105);
fitFunction->SetParameters(p0, p1, p2, p3, p4);
hist->Fit("fitFunction");
```

But I am finding it hard to set the initial values p0…p4. First of, I am not sure what they refer to, since I couldn’t find the explicit definition of the “crystalball” function, and second, most examples I have seen fit around 0 so I am a bit confused.

I would appreciate it if you could help me understand and find the appropriate parameters, thank you!