On a shift gauge, the primary arc is the reference. Editorial notes about secondary hours start from that arc rather than from a blank week. The choice is methodological: most survey instruments already designate a main job, then ask about other jobs. Treating the main shift as movable copy would invert the instrument’s own hierarchy.
In the CPS, respondents who report more than one job identify which job is the main job—usually the one with the greater hours. Hours on that job form the primary reading. Hours on other jobs are residual. Kimmel and Conway, among others writing on moonlighting in labor economics, treat that residual as the analytic object while holding main-job hours as a baseline covariate. The dial metaphor follows the same order: fix the main hand, then ask what sits outside it.
Fixing the arc also disciplines language about “extra” work. If every discussion begins by shrinking the primary shift, the free window is created by subtraction from contracted hours rather than by marking leftover sectors. Published contracts and scheduled shifts are not always flexible in the way popular copy implies. Shift Gauge therefore refuses to narrate a primary arc as soft clay. The arc is recorded as reported; secondary spells are discussed only in the remaining face.
There is an important limit. Some workers have unstable main schedules—on-call retail, rotating health shifts, gig-primary arrangements. In those cases the “fixed” arc is fixed only within a reference week, not across months. Lambert and colleagues’ research on schedule instability in hourly retail documents that unpredictability. When Shift Gauge cites such work, the primary arc is still the week’s main reported job, but the note states that week-to-week movement of that arc is part of the measurement problem.
Platform research complicates the picture further. Katz and Krueger’s work on alternative work arrangements, and later official Contingent Worker Supplement modules, show that arrangement labels and hour totals do not always land on the same mark. A person may report a traditional main job and a platform spell, or a platform spell as the only job. The fixed-arc rule still helps: first identify what the instrument called primary, then locate other spells relative to that hand.
Editorial practice under this rule looks plain. A note names the main-job definition used by the source. It reports secondary hours as a separate sector. It does not instruct a reader to shorten a contracted shift. It does not present overlapping spells as free windows. Overlap is labeled overlap.
Why insist on the metaphor at all? Because secondary-earnings copy often collapses into a single smear across the week face. A gauge with a fixed primary arc forces the writer to say where the secondary mark sits. That spatial honesty is the whole point of Shift Gauge’s line—distinct from metaphors that measure depth of pay or that clamp a bar across hours. Here the object is the dial’s open sector beside a held main hand.
No earnings outcome is attached to holding the arc fixed. The rule is for reading published instruments, not for redesigning a household’s week.