What is the significance of placing a stone on a grave when you vist the cemetery. Thank you

If a person has a choice between two ways of doing a mitvah, but one is more expensive, and more convinient ("roll-out" schach, or Chanukah glasses with pre-filled oil), does this also go in the category of Yom Tov expenses, vis a vis being paid back Min Hashomayim?

I recently attended an orthodox funeral but the male son was not allowed to follow his father's coffin. Please explain why.

I am an Electrical Engineer and Computer Scientist and I guess I really do not understand the principles behind some the Shabbat Halacha. So I would appreciate not only the Halachic response permitted or not permitted but the full reasoning behind the answer including the references. The question deals with heating water on Shabbat. My naive understanding is that any act a person does on Shabbat that causes water that is cold to heat up is not permitted. Now consider a hot water heating system. It would not be unusual for water in the system to cool down to below 113 degree F and then have the thermostat turn the system on. When it does, the water will get heated to around 180 degrees and this is heating of water on Shabbat. (A similar situation is the steam heating system.) If one argues that this is permitted because it happens automatically. The program for the home heating system is the setting of the thermostat and that was done before Shabbat. Changing the setting of the themostat on Shabbat is presumably not permitted. So I can understand this argument. No action was done on Shabbat to directly cause the heating of water. Now consider a second case. A person programs an automatic coffee maker to begin to brew coffee at noon on Shabbat The water in the coffee maker is cold. Essentially a timer is set before Shabbat that turns on the coffee maker at an appropriate time on Shabbat. (By the way I have no interest in coffee on Shabbat: I do not drink coffee or tea.) So this case if I reason from what is permitted to automatically be done should be permitted. But I have observed people do not do this and I suspect the halacha is that it is not permitted. So for me, there are two systems that from an engineering point of view are similar and yet I suspect that the Halacha for each is different. Please tell me whether this is indeed so and if so please explain why. Thankyou very much for answering the question.

why jewish calander is based on lunar and not soloar and why a comination is better, it does not make sense to me that we have one day and two days rosh chodes. similary in the moslem calander they donot know when to celebrate their holiday. in Isreal some keep tow days for sukoot and sone one day, some travel there and they say we have our parents liveing in Isreal so we keep only one day, this is very funny and in acurate thansk