When power meters are enabled, Rack measures the amount of time spent processing each module in mS (millisamples). In many ways, this is analogous to the module power limit imposed by hardware modular synthesizers in mA (milliamperes).
To maintain a stable audio clock, the total amount of time spent processing all modules must equal 1000 mS. To achieve this, the Audio module from Core uses your audio device's high-precision clock to regulate Rack's processing loop, so it idles for some amount of mS until this total is met. If the Audio idle time falls close to an average of 0 mS over its block size, an audio stutter may occur. This can be caused by other modules consuming lots of mS.
Rack advances the state of each module by the duration specified by Rack's internal sample rate. A higher sample rate decreases the timestep, resulting in more accurate analog circuit modeling at the expensive of more mS consumed by all modules.