The ONLY thing you really need is a combination of knowledge and power. As for tools, just find a way to count reps effectively. You just have to know how many reps you are doing.
Any method that does not require distraction from work is fine. In the total absence of means, in the past I got to the point of adding numbers on the calculator when I didn't have my phone with the counter app to count reps. When I also lost my calculator I got to the point of writing 216 lines on a sheet of paper and gradually erasing them while I vibrated.
Sometimes I even counted with my fingers, one hand for the units (0-9) and the other for the tens (10-100), opening all my fingers was five reps for example and closing them all was another five. Let's say that the rosary is useful in the sense that you are less distracted because you simply have to slide your fingers over the beads.
On cell phones there are apps to count reps where, by pressing the screen, it adds a rep. Usually you have to search for "counter", these apps often have this name.
About that necessary combination I was telling you about...
KNOWLEDGE:
SPIRITUAL POWER:
Start the work with knowledge and keep your energy level high by meditating. Good luck, soldier! Come back as a winner!