We may earn a commission from links on this page.Have you ever switched gyms and tried to do your usual workout, only to find that the machines are a lot harderor maybe a lot easier? Before you start questioning your strength or your training, you need to know something: you cant trust the numbers on the weight stack, and you shouldnt expect them to match from gym to gym or even machine to machine.What do the numbers on the weight stacks mean?When youre looking at a cable machine, or any type of strength training machine with a stack of rectangular weights, there is probably a little sticker on each plate with a number.Sometimes those numbers are in pounds, and they represent the weight of the plate itself. If you were to take the 10 pound plate off the machine and weigh it, it would weigh 10 pounds. (Probably.) Sometimes they are in kilograms. If it doesnt say which, theres no easy way to know for sure. It also doesnt really matter, for reasons Ill explain below.And sometimes, plate stacks arent labeled with weights at all. You just know that if youre strong enough to work with the plate labeled 5, youre stronger than if you could only use the machine at the 4 setting. How many pounds are you lifting? Its not telling, and to be honest it doesnt matter.Pulleys and levers change how heavy the weight feelsEven when the numbers on the machine are accurate, theyre not really helpful. Lets say theres a cable stack where each plate is 10 pounds, and you can use 5 plates for a certain exercise. You are moving 50 pounds of iron.But are you really applying 50 pounds of force to move that iron? Not necessarily. As you may or may not remember from your school days, pulleys and levers can make it easier or harder to move a weight. If youre doing a cable crossover on a LifeFitness Signature Series Dual Adjustable Pulley machine, the one below, youre getting a 4:1 mechanical advantage. When you put the pin in the stack where it says 52.5 pounds, you may be lifting 52.5 pounds but you only need about 13 pounds of force to do that. Cable machines are simple enough that a company can publish their ratio, like LifeFitness did. (For some more examples: Reps Athena pulley system has a 2:1 ratio, so that 20 pounds feels like 10 pounds, whereas their lat pulldown has a 1:1 ratio, so 10 pounds feels like 10 pounds.)But when it comes to other types of machines, there may not be a simple answer. A given gym contraption may have a combination of pulleys, levers, and other devices, and they may provide different amounts of assistance depending on how you adjust the machine or what exercises you are doing.Machines have different designs (and maintenance schedules)With all of that in mind, you now know that the weight you feel like youre moving is different from the weight labeled on the stack. But what does that tell us about comparing one machine to another?Machines can have different designs, especially if they are different models or come from different manufacturers. One gym might have a 4:1 cable machine, while another might have a similar machine with a 2:1 ratio. One gyms leg press might be a horizontal style with a weight stack, while another is an angled leg press that you load with plates from the free weight section. You shouldnt expect 200 pounds on one to feel like 200 pounds on the other.Even when two gyms have the exact same make and model of machine, one may be harder to move than the other. Maybe Gym A has an older machine thats built up some rust, while Gym B has a newer model that was just oiled yesterday.How to track your progress when you train on different machinesNow that we know that every machine is different, and the labels dont necessarily mean what they say, how are you supposed to handle that?Unfortunately, theres no simple solution. If you alternate between two gyms, your best bet is to keep notes separately for each one. In your notebook or your strength training app, just track leg press Planet Fitness as separate from leg press Crunch. (Most apps will let you duplicate and edit the exercise entries.)If you drop into a variety of mystery gymsmaybe you travel a lottry programming your workouts by RPE. Instead of doing four sets of 12 reps of 70 pounds, think of it as four sets of 12 reps at an 8-out-of-10 difficulty. That might be 70 pounds on the stack at one gym, 65 at another, and 72.5 at a third, but it doesnt matter. Youll still be getting a good workout at all three.