I am self studying thermodynamics and I stumbled upon the concept of a quasi-equilibrium process which I dont fully understand but here are my thoughts, Equilibrium is a condition of balance characterized by the absence of driving potentials and at such conditions you can measure properties that describe the state of a system and that these properties are the same at every point in a system. This can be validated if our measurements don't diverge, if they were then we not at equilibrium. If a system undergoes a certain process, we are not in equilibrium, so how can we trace the path from one state to another ( namely the properties that describe the system are changing with time how can they be quantified) . In order for us to take measurements the system has to be in equilibrium, but again if we leave the system to come to equilibrium how can we be sure that the properties that describe the system in equilibrium are the same as those that described it at the point we decided to stop the process? To illustrate what I am trying to say in the last two sentences suppose I have a cup of water and I am heating it and I place a thermometer inside the cup of water to measure its temperature, the reading would be misleading, the water temperature close to the heat source would be higher than at the top and If I stop heating to allow the cup of water to reach equilibrium and again take a measurement of the temperature that reading would be different than my previous reading I allowed my cup of water to exchange heat with the surrounding. If we allow for an infinitesimal change in the set of properties that describe the current state of our system, we are guaranteed a process but why is this process slow, and how if we lump those assumptions allow us to take measurements that are representative of the system?