In modern society there is a growing preference for studying the mind from an experiential or practical level, rather than from an academic or theoretical one. Although it is important to engage in ‘Periodic Practice’ (Fixed-Term Training) by entering a professing training center and temporarily leaving behind one’s routine life, what is equally important is setting up a ‘Regular Practice’ (Daily Training) or a ‘Mind Practice in Daily Life,’ that integrates and is carried out in one’s life without abandoning one’s home or work environment. Won-Buddhism established a teaching based on the buddhadharma suitable for this era, lifestyle, and public. Sotaesan enacted the ‘Dharma of Training’ in order to study the buddhadharma and apply it in one’s life regardless of whether one is ordained or lay. Among his teachings, Sotaesan taught the ‘Practice of Checking Mindfulness and Unmindfulness’ (abbreviation. PMU) designed to directly study the mind when faced with ‘Sensory Conditions (境界)’ in daily life. PMU follows three requirements: First is ‘preparation practice,’ which means setting up in advance ‘an article to do’ and ‘an article not to do.’ Second is ‘action practice,’ which means going on with one’s daily activities keeping in mind the pre-defined articles and ‘making choices with sound thought.’ Third is ‘reflection practice,’ which means investigating one’s level of study by accessing whether one was ‘mindfulness’ (有念), if making choices with heedfulness or ‘unmindfulness’ (無念), if making choices without heedfulness. These three points correspond with articles [1, 2, 6] of the ‘Items of Heedfulness in Daily Applications’ in the section called ‘The Method of Daily Training.’ Therefore, the PMU contains the basic pattern [or article 2.→article 1.→article 6. in ‘Item of Heedfulness in Daily Applications’] of daily study. Furthermore, the scope of the study expands by repeating ‘when to act’ and ‘when to rest,’ finally connecting mind study with the teaching on ‘Timeless Sǒn (無時禪)ㆍPlaceless Sǒn (無處禪).’ The PMU that carries out ‘The Method to Assess Mindfulness or Unmindfulness’ was practiced most widely in small edification groups composed of ten people called Tan around 1925. However, ‘The Method of Keeping a Dairy’ formally took effect around 1928, and since that time up until now ‘The Method to Assess Mindfulness or Unmindfulness’ has been considered a more basic method than that of keeping a diary. However when the PMU is practiced at a deep level it takes on a completely new aspect. At the beginners level, the PMU depends on outside sensory conditions, but at the level of an adept, that practice depends on the inner state of the mind. So the scope of access greatly expands and the person at this level only studies how they are using their mind and body when in action or at rest without having to leave the original mind [or the self-nature of the void or calm and numinous awareness]. Therefore it becomes a living practice in which a person does not leave their original mind in daily life. PMU presents the most basic patterns in everyday life, making choices in action to progress the threefold study together, at the same time. And ultimately, anyone can do ‘mind practice’ regardless of time or place.