[Free42] root finder

[Marcio]

I have been playing with the Free42 app lately and must say it's of superb quality. The option to change GUI is also top-notch.

Anyway, while programming it to find zeros of equations, I noticed something interesting:

On page 184 of the 15C's user guide, one can find the following equation:
\[h = 5000\left(1-e^{-t/20}\right)-200t \]
which is solved for \(t\) when \(h=0\). The 15C manual recommends 5 and 6 as initial estimates. In fact, if the estimates are smaller than 4, it will converge to zero (which is also correct), and that was when I suspected Free42's solver was keeping some sort of cache. No matter what other values I entered for \(t\), the app wouldn't find the the root for \(t>0\), which is 9.2843...

A work-around is to integrate the function (ie the program), which somehow clears the "cache", and then solve for \(t\) again.

Is this a feature or an oddity/bug? Or did I miss something?

Thanks.