To measure distances right click in the JSmol window and

scroll down to "Measurements". The arrow will reveal more options.

Select "Click for distance measurement". Then click on the relevant

atoms to determine the distance between them. You can continue

to click on further atoms and the distance will be shown in nm.

Measure the distances (in nm) between the zinc atom and the closest

nitrogen for each of the three histidine residues. These are

typical distances for coordination bonds. Average these three distances.

Also measure the distance between the oxygen (coordinated water) and the Zinc

atom.

Atom colours: Carbon - grey; Oxygen - red; Nitrogen - blue; Zinc - blue/grey
Hydrogen atoms have been removed for clarity.