Example: Mathematically speaking, the vector ( cos ⁡ ⁡ ( t ) , sin ⁡ ⁡ ( t ) ) has a positive frequency of +1 radian per unit of time and rotates counterclockwise around the unit circle, while the vector ( cos ⁡ ⁡ ( − − t ) , sin ⁡ ⁡ ( − − t ) ) has a negative frequency of -1 radian per unit of time, which rotates clockwise instead.