Accuracy as you've put it, I'm assuming is in reference to actual PDGA ratings.
The accuracy of ESC
round ratings depends primarily on how well the SSA is set for the course on easyscorecard.net (or in your own app), but also depends on the playing conditions of your round vs. what the SSA reflects.
E.g.'s
If the course, under typical conditions, has an SSA of 49... but for some reason the SSA in your app is set to 53, then you're going to get inflated
round ratings.
If the course, under typical conditions, has an SSA of 49... but it's pouring down rain with blustering wind when you play then you're going to get deflated
round ratings.
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PDGA ratings are "accurate" because the SSA is unique for each round and is calculated from the scores of the players in that round. SSA can easily vary one or two strokes from round to round which translates to ~10-20 ratings points.
As I said above: the key to getting generally accurate ratings from ESC is making sure the SSA you use is reflective of the conditions you played. For the Houston courses I try to keep the easyscorecard.net SSA's updated with typical condition tournament values.
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The last thing to consider is how
Player ratings are calculated. In short, the PDGA uses your last ~12 months, double weights the most recent 25%, and throws out exceptionally low rounds. IIRC ESC is using all rounds from the last 180 days unless you specifically mark the round as a "practice round" in the Properties->Advanced Options menu. Practice rounds are not factored into ESC
Player ratings.
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FYI, with 115 rounds in ESC for 2012 (not sure how many in the last six months) I'm listed with a 940 player rating. On the PDGA ratings update this week I went from 941 to 946. To me that seems pretty darn accurate.