How has the scanning tunneling microscope become useful in estimating the size of an atom?

(N/A) The scanning tunneling microscope $(STM)$ is a powerful instrument developed for the study of nanotechnology and surface science.
It operates on the principle of quantum tunneling,where electrons tunnel through a potential barrier between a sharp metallic tip and a conducting surface.
Because the tunneling current is extremely sensitive to the distance between the tip and the surface,the $STM$ can achieve a spatial resolution of better than $1 \; \mathring{A}$.
This high resolution allows scientists to image individual atoms and map their positions on a surface,thereby enabling the direct estimation of the size of an atom.