Mismatch Dimension after Extrude Cut

As in the title, after I finished the sketch with my desired dimensions, I used the extrude cut feature. However, as shown in the figures below, the dimensions of my sketch do not match the dimensions after I extrude cut. A 30mm became 30.04mm after the extrude cut. Not sure what the problem here is, and I also attached my sldprt file for inspection. 

SolidworksParts And Features