to heft, to hold or weigh in the palm
掂 centers on testing weight by hand: hefting something or holding it in the palm to feel its heft.
掂 combines 扌 (hand) with 店, which likely contributes the sound. The character is used for weighing or hefting by hand.
A hand 扌 beside a shop 店: imagine a customer hefting goods in a shop to test their weight.
For テン, picture a shopkeeper using a hand to weigh ten items: ten -> テン, and the hand hefts each one.