if Sevvai (Mars in English and sevvai in Tamil) is in the 7th, 8th houses from the Lagna or Chandran or Sukran, the horoscope is supposed to suffer from Sevvai Dosham. A horoscope with Sevvai Dosham should not be considered as matching for marriage with a horoscope which does not suffer from Sevvai Dosham. This is the general rule. If a horoscope with Sevvai Dosham is married to a horoscope without Sevvai Dosham, it is feared that the life of the spouse will be endangered. Now it need not necessarily be a demise. In modern days, it can be taken the other way around also. In the case of incompatible Sevvai Doshams, it may, instead of risking the life of the spouse, may result in a long term separation, legal separation (divorce) or frequently disrupted marital relationships, taking away the peace of mind.
Chevvai Peyarchi 2018 and Mercury transit information is provided in ePanchang along with details about other planetary movement; this is available online and free for users