Average+ is a crudely normalized index of total pinfall, so 100 is exactly equal to the entire field's average. If the field averages 210 and I average 231, then my Average+ is 110 (231 * 100 / 210 = 110).

Lane Effects is an attempt to normalize pinfall for the bowling center. We don't have enough data to normalize to a neutral bowling center, but we can at least compensate for the field's average scores at the various centers, so if the field averaged 220 in center A and 200 in center B, then a 220 game in center A and a 200 game in center B are both normalized to 210 (the overall average between the two centers).