This is a momentum indicator of the volume's strength index. The "concept" is taken from the RSI although the formulation is not anything close to it !!!
The concept of RSI is that we take the strength of the price and show it as an oscillator, this will show the balance of strength between buyers and seller.
In Volume Strength Momentum, the concept is to find the strength balance between selling and buying volume and calculate the momentum of it. This will become another leading indicator that shows possible critical moments that we can have a shift of strength on volume.
The formula for the strength and momentum calculation is original and not related to rsi in any shape or form.