There are 10 skills listed in sim's skill journal like cooking or logic. They are "official" skills.

I guess that there are some additional "hidden" skills that sim can practice and horn it to change game behavior or for better outcome, but that does not shown in skill journal. I remember that Sims 2 had invisible "dance" skill, too. It seems that Sims 3 has hidden chess skill. I suspects skill scores like joke, kiss, finding other's trait, etc...

Did anyone find list of such "hidden" skills in TS3 ? Or confirmed ones by examining game resource data files?

There are tons...the game keeps count of how many times a Sim has made a certain food, so that each time it is more likely to be of better quality, for example.

There are many hidden skills.

Some are associated with the career.

If your sim have a police career, there is a skill called "Keep them guessing" that he/she can learn.

Yep and the more you get of the charisma skills, the more different types of greetings and conversations that you can have with the other sims, including being a comedian if you do a lot of jokes and funny stories.

I didn't mean "secondary skills" like cooking individual food or greeting unlock.
I mean independent "primary skill". Plying chess improves logic skill. But it seems that mastering logic skill to max 10 level (by reading logic study books) does not render excellent chess winning probability. I'm not talking about tournament ranking. To improve chess skill, sim must practice/play chess actally. Likewise, dance skill improves only by actually dancing. I guess that independent chess skill and dance skill scores are kept for each sim.

Chess skill is one of the skills of logic if you look in the logic handbook of the skill's panel. So it wouldn't be a hidden skill if you are comparing it to the other skills gained from the primary skills. I haven't looked at the virtuoso or artistic skill books to know what their have for extra skill building but dance could be in one of them.

I really hope dancing is a hidden skill! I'd hate to see them all doing the same things over and over. But I thought dancing in TS2 was related to their "Music & Dance" hobby (Freetime)? Isn't that how you unlock that "Bust-A-Move" option?

I am not talking about chess ranking which is displayed in logic skill journal.
If your sim never join qualifying chess game for chess tournament, your chess ranking remains zero(0) level regardless of how much chess game you sim played with your friend sims and win many many times. So there must be separate chess skill variable independent of logic skill or chess ranking.

Higher logic skill level may help chess winning ratio. But even if your sim started first chess practice after maxed out logic skill ( so no more improvement from higher logic skill), it seems that winning ratio improves considrably by playing practicing chess.

My sim has played chess in the park with friends and strangers even when the opportunity for the chess tournament was off and his wins and losses from that still show up in the skills guide.

Is the winning ratio ( win count vs defeat count ) chess skill? I don't think so. Then just practicing chess personally without actually playing game with other sims should not improve chess skill. Practicing chess alone do improves chess skill even after maxed out logic skill.

I can take a screenshot if you wish? He hasn't played in the tournament yet. I've sent him to the park in the mornings to meet new people in order to get his charisma level maxed and a few he played chess with and the 4 wins and 1 loss he got from that shows up in his skills guide for logic.

I know that the chess win count record is shown in logic skill jounal.
But I don't think is is directly proportional to internal "chess skill" variable that affects dice-rolling for deciding winner.
It is just record of game history, not skill point.

It goes toward getting opportunities and for the special skill building challenges you get with each primary skill.

I read about this in the game guide.

There are a few hidden skills, like chess and individual recipes Their progress isn't tracked anymore, but the more you do them, the better you get.

If your Sim plays chess a lot, they'll start to win more.
If your Sim cooks waffles a lot, their waffles will become higher quality.

I think that "hacking" is yet another hidden skill. The longer time you spend for hacking computer, the more money you can get from hacking. It does not show up in skill journal. You need computer wiz trait to do hacking at night time.

Does the game guide list any other hidden skills?