In the equation $X = G^{1/2} h^{1/2} c^{-5/2}$, where $G$ is the universal gravitational constant, $h$ is Planck's constant, and $c$ is the velocity of light, the dimensions of $X$ match those of:
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This expression defines the standard Planck Length ($l_P = \sqrt{\frac{G\hbar}{c^3}}$). Recognizing this combination of fundamental constants allows you to identify its dimension as length immediately, bypassing the tedious process of tracking individual exponents for mass, length, and time.