Trying to understand the fitting plots

[ralphflat]

I have used the fitting functionality to try and find reasonably values for some of the parameters. Below is the plot that resulted. I don't understand what the red and black lines are. The output of the analysis seems to be the black line.

8996 87.195699 270.120662 -135644.584362
8997 87.195699 270.120662 -135644.584362
8998 87.195699 270.120662 -135644.584362
[8999 rows x 3 columns]
Trace 8999
tilt_deg 87.19±0.011
heading_deg 270.07±0.031
B

See also #12 and #13