The number is the distance, in millimetres from the fret to the bridge for a standard scale length guitar.

Scale length 640.00
Fret Posn
-8 1015.94
-7 958.92
-6 905.10
-5 854.30
-4 806.35
-3 761.09
-2 718.38
-1 678.06
0 640.00
1 604.08
2 570.18
3 538.17
4 507.97
5 479.46
6 452.55
7 427.15
8 403.17
9 380.55
10 359.19
11 339.03
12 320.00
13 302.04
14 285.09
15 269.09
16 253.98
17 239.73
18 226.27
19 213.57
20 201.59
21 190.27
22 179.59
23 169.51
24 160.00
25 151.02
26 142.54