A detector frame is an indexed grid of physical measurements. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Detector pixels are indexed

The schematic detector has 4 rows and 5 columns.

rows=4,cols=5\text{rows}=4,\quad \text{cols}=5
Indexed throughputIndexed measurements become exact count budgets.indexed readout

Rows times columns gives pixels

The exact pixel address count is 20.

Npixels=45=20N_{\text{pixels}}=4\cdot5=20
Indexed throughputIndexed measurements become exact count budgets.indexed readout