# How is the Hartree accuracy calculated between the exact and VQE results?

In the Simulating Molecules using VQE section of the Qiskit textbook it states an accuracy of $$0.0016$$ Hartree between the exact and VQE results with Hartree energy values of $$-1.86712098$$ and $$-1.80040360007339$$ for the ground state of $$H_2$$, respectively.

How is $$0.0016$$ computed? and is it an error metric similar to absolute error?