A Pendulum Summon (ペンデュラム召(しょう)喚(かん) (Ｐ(ペンデュラム)召(しょう)喚(かん) in the card text) Pendyuramu Shōkan) is a form of Special Summon introduced in . Pendulum Summoning allows the player to Summon high-Level monsters.
Once per turn, during their Main Phase, if the turn player has a Pendulum Monster in both Pendulum Zones, that player can Pendulum Summon any number of monsters from their hand and/or any number of Pendulum Monsters from their Extra Deck with a Level between the blue Pendulum Scale of the Pendulum Monster in the left Pendulum Zone and the red Pendulum Scale of the Pendulum Monster in the right Pendulum Zone. A Pendulum Summon can be negated by cards that negate Special Summons like " " and " "; however, if more than 1 monster would be Pendulum Summoned at the same time, then cards like " " or " " that specify they can only be activated when exactly 1 monster would be Summoned cannot be activated.
Since only monsters whose Levels are between the Pendulum Scales of the 2 Pendulum Monsters in the Pendulum Zones can be Pendulum Summoned, if they have Pendulum Scales that are either the same or have a difference of 1, you cannot perform a Pendulum Summon, because there is no Level number that exists between them. (Even if you cannot perform a Pendulum Summon, you still gain the Pendulum Effects of the Pendulum Monsters in the Pendulum Zones.)