Mental Log Easy
The performer shows the spectators four small rods with four different numbers on each of their sides. The spectator is invited to toss the rods on the table, assemble them, and then sum up on a Calculator (or on their telephone) the 16 numbers on the top sides of the rods.
While the spectator is starting to just digit the first number, the performer immediately calls out the total! This can be repeated as many times as desired, and always with a different result.
The effect for the spectators is that you are a human computer able to add many different numbers in the blink of an eye.
Nice trick, good price!