Hi Devoted,
Please have a look into the Formula Effector> Effector> f-Frequency.
The values that are used there are the ID numbers of the letters. It starts with zero. Set the values as linear interpolation for equal progress of writing.
The Formula-Effector is set to determine the Visibility of the Clones [Parameter Tab].
The formula itself is simple ID<f. Which means, if the ID of the clones is smaller than f, then it produces a value one, as it is true. Otherwise, the result is zero, as in not true. This, in return, determines the visibility. A value of one equals visible, a value of zero sets it to invisible.
The Formula Effector is used in the Letter Tab.
Scene file
https://www.amazon.com/clouddrive/share/qvSiYQskWVbwJs1QE2wJCq3G37BbQM4SRqi1N4a6mAI
All the best