I'm confused as to what starEventChance and starAutoSuccessChance mean for the Observatory. If they're just percentages, why wouldn't there be a percentage sign? And a 20% increase in chance grows quickly, even if there's diminishing returns (ref.). So this doesn't seem to be the right interpretation.

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Question: What do starEventChance and starAutoSuccessChance mean for the Observatory?

2 Answers 2


starAutoSuccessChance increases the chance that an astronomical event succeeds automatically. The value there does end up operating as a percentage. The automatic success increases by 1% for every Observatory. So if you had 20 Observatories, you would get an automatic success on average 1 in 5 events, 20%. I believe this is subject to diminishing returns, but there is a workshop upgrade that provides 100% automatic success long before you should have 100 Observatories to test it. (There is actually another answer which details the formula behind it here.)

starEventChance increases another variable in the same way for providing the astronimcal events in the first place. Trying to find a formula to translate what the value would do, but the base chance is supposed to 0.25% per day. I believe the 20 would simply add on to that (making 0.45% per day, and climbing upward from there).


In additions to Radhil's answer, the starEventChance indicates the chance to get a star on a given day. The base chance is indeed 0.25%. Every 20 points increase the chance by 0.20%. This is because chance, the variable in the source code, is compared with a random integer between 0 and 10000. The relevant code is below (I omitted quite some stuff, but it's not necessary for your question).

var chance = 25;    //25 OPTK of event per day  (0.25%)
chance += this.game.bld.getEffect("starEventChance");

if (this.game.rand(10000) < chance && this.game.bld.get("library").val > 0){
    var autoChance = this.game.bld.getEffect("starAutoSuccessChance");  //in %
    var rand = this.game.rand(100);

    if(rand <= autoChance){
        dojo.hitch(this, this.observeHandler)({}, true);

So starEventChance is in hundredths of percentages, giving 0.20% bonus for each 20 points, and starAutoSuccessChance is in percentages, yielding 1 extra procent chance of automatically succeeding a celestial event for each Observatory you buy.

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