http://doc.qt.digia.com/4.6/qtglobal.html#qreal-typedef
typedef qreal
Typedef for double on all platforms except for those using CPUs with ARM architectures. On ARM-based platforms, qreal is a typedef for float for performance reasons.
This still seems to be the case for 4.8 as well.
This lead to the following compile error on arm in kst:
/builddir/build/BUILD/kst-2.0.7/src/libkstapp/plotrenderitem.cpp:561:33: error: no matching function for call to 'qMin(double&, qreal)' y = qMin(y, plotItem()->yMax()); ^
If there is scientific type codes using qreal this might lead to some precision issues as well.
Is double really that much slower on arm?