SMath doesn't understand femtoamps. I found the Units.xml file and it only defines from pico- to tera-
<prefixes>
<add factor="1" exp="-12" name="p pico" lang:rus="п пико" />
<add factor="1" exp="-9" name="n nano" lang:rus="н нано" />
<add factor="1" exp="-6" name="μ micro" lang:rus="мк микро" />
<add factor="1" exp="-3" name="m milli" lang:rus="м милли" />
<add factor="1" exp="-2" name="c centi" lang:rus="с санти" />
<add factor="1" exp="-1" name="d deci" lang:rus="д деци" />
<add factor="1" exp="1" name="da deka" lang:rus="да дека" />
<add factor="1" exp="2" name="h hecto" lang:rus="г гекто" />
<add factor="1" exp="3" name="k kilo" lang:rus="к кило" />
<add factor="1" exp="6" name="M mega" lang:rus="М мега" />
<add factor="1" exp="9" name="G giga" lang:rus="Г гига" />
<add factor="1" exp="12" name="T tera" lang:rus="Т тера" />
<add factor="2^10" name="ki kibi" lang:rus="ки киби" />
<add factor="2^20" name="Mi mebi" lang:rus="Ми меби" />
<add factor="2^30" name="Gi gibi" lang:rus="Ги гиби" />
<add factor="2^40" name="Ti tebi" lang:rus="Ти теби" />
</prefixes>
Can you add all SI prefixes from yocto- to yotta-?