In the Simple Units environment, the piecewise function is modified so that it verifies that the values it can return have the same dimension.

Every command in the Simple Units environment that needs to determine whether an expression is valid or not, does so using the Units:-TestDimensions command.

$\mathrm{with}\left(\mathrm{Units}\left[\mathrm{Simple}\right]\right)\:$

$\mathrm{piecewise}\left(x<1\&comma;2\mathrm{Unit}\left(m\right)\&comma;3\mathrm{Unit}\left(\mathrm{ft}\right)\right)$

$\left(\left\{\begin{array}{cc}2& x<1\\ \frac{1143}{1250}& \mathrm{otherwise}\end{array}\right.\right)⟦m⟧$

$\mathrm{piecewise}\left(x<20\mathrm{Unit}\left(m\right)\&comma;2\mathrm{Unit}\left(\mathrm{bar}\right)\&comma;x<40\mathrm{Unit}\left(m\right)\&comma;35\mathrm{Unit}\left(\mathrm{inch\_mercury}\right)\&comma;3\mathrm{Unit}\left(\mathrm{gigadyne}\right)\right)$

Error, (in Units:-Simple:-piecewise) the following expressions imply incompatible dimensions: {piecewise(Units:-Simple:-`<`(x,Units:-Simple:-`*`(20,Units:-Unit(m))),200000*Units:-Unit(Pa),Units:-Simple:-`<`(x,Units:-Simple:-`*`(40,Units:-Unit(m))),18015585/152*Units:-Unit(Pa),30000*Units:-Unit(N))}