The state of strain at a point in a machine component is given as
\[
\varepsilon_{xx} = 2.5 \times 10^{-4}, \varepsilon_{yy} = 2.0 \times 10^{-4}, \varepsilon_{zz} = -1.5 \times 10^{-4},
\]
\[
\varepsilon_{xy} = 2.5 \times 10^{-4}, \varepsilon_{yz} = -0.5 \times 10^{-4}, \varepsilon_{zx} = -1.0 \times 10^{-4}.
\]
The volumetric strain at this point is .............