If the input signal u is constant and it is different from starting delayed input d, the middle value between u and d will be reached after HalfTime.
The mathematical background:
d'(t) = k*(u(t) - d(t)) => The solution of d(t) in special case, if u(t) is constant at each time t: d(t)=u+(d(0)-u)*e^(-k*t), where the definition of HalfTime is d(HalfTime) = d(0) + (d(0)-u)/2.
2009-2018
Marek Matejak, marek@matfyz.cz