Notation and units — 20 Watts Was Enough

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System variables

Symbol	Meaning	Unit
$x$	one input event or task instance	declared by task
$Q$	task-quality measure	task-specific
$R$	risk, error, or miscalibration measure	task-specific
$L_{p95}$	95th-percentile end-to-end latency	seconds
$E$	energy over a declared interval	joules
$P$	average power over a declared interval	watts = joules/second
$T$	measurement duration	seconds
$N$	qualified events completed	count
$B$	bytes transferred across a named boundary	bytes
$C$	counted arithmetic or module work	declared operation
$g_i(x)$	gate for module $i$ on event $x$	dimensionless
$c_i(x)$	cost proxy for module $i$	operations, bytes, or joules
$z_t$	latent state at time $t$	dimensionless vector
$\sigma_t$	predicted uncertainty for $z_t$	same scale as distance
$s_t$	normalized surprise	dimensionless

Symbol scope

The table above reserves unqualified project-wide symbols. A chapter may add subscripts or superscripts, but it must not reuse a reserved symbol for a different physical quantity. In particular, $P$ remains power and $s_t$ remains normalized surprise. Predictors use symbols such as $f_\theta$ , and an environment state uses a locally declared symbol such as $u_t$ .

Time durations use seconds. Discrete sequence horizons use an explicit count such as $T_\tau$ or $T_B$ rather than the unqualified duration $T$ . Every local objective must state the unit of its value and of every coefficient that makes unlike terms commensurable.

Required qualifiers

FLOP, operation, token, event, and sample are not interchangeable. Every use must define:

arithmetic precision;
dense, effective-sparse, or executed count;
training or inference;
batch and sequence shape; and
whether memory and communication are included.

Boundary labels

$E_{\text{device}}$ : accelerator package only.
$E_{\text{node}}$ : accelerator, CPU, memory, local storage, and node cooling.
$E_{\text{cluster}}$ : nodes plus network and shared infrastructure.
$E_{\text{facility}}$ : cluster energy multiplied by a contemporaneous, attributable facility overhead.

Results must not move between boundaries by implication.