To determine the dimensions of the product $CR$, we examine the dimensional formulae of capacitance ($C$) and resistance ($R$) as provided in the sources:

1. Capacitance ($C$): According to the dimensional tables, capacitance is defined as charge divided by potential difference ($Q/V$), with the dimensional formula $[M^{-1} L^{-2} T^4 A^2]$ .
2. Resistance ($R$): Resistance is defined by Ohm's law as potential difference divided by current ($V/I$), with the dimensional formula $[M L^2 T^{-3} A^{-2}]$ .

By multiplying these two formulae: $[CR] = [M^{-1} L^{-2} T^4 A^2] \times [M L^2 T^{-3} A^{-2}] = [M^0 L^0 T^1 A^0] = [T]$.

The resulting dimension $[T]$ represents the physical quantity of time or time period . In electronics, $CR$ is known as the capacitive time constant.