It was brought to my attention that several software applications already exist, that are supposed to do the job that I set out to make this software application perform. One of the authors for both of the peer-reviewed articles that I have linked to, has made several versions of an application called "SuperMemo." He also released the algorithm "SM-2," for other software developers to use if they want, which is the algorithm the majority of these applications are based on. The entire algorithm that this application implements, except for the calculation of difficulty, and the time of the first interval, is pieced together from the formulas presented in the document titled "Two components of long-term memory." The formulas in that document are for the forgetting curve, and spacing. I was able to make an algorithm, which mostly uses formulas presented in that peer-reviewed paper. Most of the software applications that have been available for a while to teach before information is forgotten, other than "SuperMemo," use the "SM-2" algorithm. "SM-2" is from 1987. It is much less precice than what was being used for the 1995 peer-reviewed experiment. The algorithm I wrote for "GlideCLI" is much more precise than "SM-2," which non-"SuperMemo" software is implementing.
I found Slope-Intercept to calculate difficulty, filled the gap perfectly for the major piece I was missing for the algorithm to be complete. I even found that the best range of values for the difficulty variable, is between 1.3, and 2.5. Difficulty will be calculated only within the constraints of that range, by using the Slope-Intercept formula. The calculation of difficulty in the peer-reviewed paper titled "Optimization of repetition spacing in the practice of learning", is not only more complex, but it is less accurate because it can produce values that are outside of the range of values that are needed for the entire algorithm to work. This means that every value that the formula from that paper produces, is not a value that can be used accurately. "SM-2", and the rest of the algorithms other than the one used in Glide, "fix" this inaccuracy by using the following logic:
"If EF is less than 1.3 then let EF be 1.3"
This means that an engram with a higher difficulty, and lower spacing interval, is upgraded to a value that an easier topic to remember would share, if that easier engram were actually calculated to be a difficulty, (same as easiness factor, or EF), of 1.3. The two would share the same length of time for the interval. This inaccuracy is why the difficulty in the "SuperMemo" family of software, must be recalculated for every repetition. They do it to compensate for the lack of precision in that measurement. By applying Slope-Intercept in place of the formula used in other software, difficulty for each item in relation to the other items, is accurate, and does not need readjustment.
GlideCLI, and Glide-UWP, both implement, and are the only ones that currently do implement this formula for the calculation of difficulty, or easiness factor.