Understand the mapability wig file values

[lethalfang]

#bedGraph section chr1:10000-81873
chr1	10000	10014	0.00277778
chr1	10014	10015	0.333333
chr1	10015	10026	0.5
chr1	10026	10031	1
chr1	10031	10036	0.5
chr1	10036	10037	0.333333
chr1	10037	10048	0.2
chr1	10048	10050	0.166667
chr1	10050	10051	0.333333

I'm trying to figure out the mapabiliity of chromosome regions.
Does anyone know what the values in the last column mean?

Thanks.