There are many types of half-arcs on guitar tabs. 1. There are s (circled or not) and sl on the semi-arc, which are portamento signs. There are several types of portamento, including strumming first and then sliding, strumming and sliding then strumming, and free portamento. General textbooks have detailed explanations. 2. There is a p on the half arc (with a circle or not), which is the hooking method. Play the first note, and the second note is drawn with your left finger. 3. There is an h on the half arc (with or without a circle), which is the hammering method. The first note is played, and the second note is struck by the fingers of the left hand. 4. If there are numbers 3, 5, 6, 7, 9... on the semi-arc, it means 3-tuplet, 5-tuplet, 6-tuplet, 7-tuplet, 9-tuplet. There are legatoes with more than one beat and legatoes with less than one beat. Play them according to the situation and the requirements of the music score. Nowadays, many legato symbols on staffs use square brackets to append numbers instead of semi-arcs, which have the same meaning. 5. There is only half an arc, no letters or numbers, it is a diacritical mark. It means that the duration of the previous note is extended to the next note, and the latter note is not played. Some semi-arcs have a very long span, even spanning a section or more, and are meant to extend the strong note, which is usually the starting note, as much as possible. In classical music, it’s called “slip.”