Well, let‘s take a look at your situation. What level are your athletes or clients at? New athletes or clients probably would not benefit from percentages as much as more advanced clients, as they need to learn how to perform the lift correctly first and foremost. Second, a new client will adapt to the exercise so fast that by the next time you perform the exercise, their 1 rep max may be out of date and thus their percentages would be incorrect (if they used to bench 100lbs, but after 2 workouts they can bench 110lbs, that 60% you have them working out as now too low to cause the adaptation you are looking for).
Microsoft Excel is a fantastic tool for analyzing scientific data. Microsoft Word is a fantastic tool for writing up scientific research. So surely Microsoft Office is the only software a scientist would ever require beyond that associated with specialist scientific apparatus? Unfortunately, that has never been the case and most university researchers would identify one big problem with the Office suite and that is why it‘s always been difficult to present formulas in Word and Excel. Even when you type a simple fraction like 3/5, it gets presented on a single line. As for Greek symbols like pi...well, that would mean many hours wasted trawling through Excel‘s Insert Symbol menu.