@KK The titration procedure provides a scaling factor that must be applied to the stimulation source (incident E-field, input current, or voltage applied at electrode pairs) in order to initiate an action potential in a fiber or neuron.
Here are some examples depending on the stimulation source:
Source: Incident E-field (e.g., induced by TMS)
Assume the incident electric field is 1 V/m, and the titration procedure yields a titration factor, tf.
The threshold E-field is therefore tf [V/m].
If this 1 V/m field results from a coil current rate of change dI/dt = A [A/s], then the threshold dI/dt required is A × tf [A/s].
Source: Applied voltage
Let the applied voltage across an electrode pair be V = V₀. This value is also used as the Dirichlet boundary condition in low-frequency (LF) simulations.
If the titration factor is tf, the threshold voltage becomes V₀ × tf [V].
Source: Applied current
Let the applied current to an electrode pair be I = I₀, typically derived from LF simulations via a current flux integrator.
With a titration factor tf, the threshold current is I₀ × tf [A].
The titration factor tf is a dimensionless number that gains physical meaning when applied to the relevant stimulation quantity (electric field, voltage, or current).
@LJ was suggesting the correct course of action. I hope this clarification is helpful!
