  The Infinitesimal Calculus explores mainly two measurements: the
instantaneous rates of change and the accumulation of quantities. This work
shows that scientists, engineers, mathematicians, and teachers increasingly
apply another change measurements tool: functions' local trends. While it seems
to be a special case of the rate (via the derivative sign), this work proposes
a separate and favorable mathematical framework for the trend, called
Semi-discrete Calculus.
