Calibration Schedules for Clinical Scales

Scales lose accuracy gradually — through load cell fatigue, temperature cycling, knocks and being moved. Nothing on the display announces it.

The schedule

Daily, before the first patient. Check the spirit level is centred and the display reads zero with nothing on the platform. Two seconds, and it catches most day-to-day problems.

Weekly. Place a known weight — a labelled test weight, or anything of a verified constant mass kept for the purpose — and confirm the reading. Consistency over time is what you are watching for.

Annually, at minimum. Full calibration by a competent service against traceable reference weights, across the weighing range rather than at a single point.

Immediately after any drop, any move to another room, or any reading that looks implausible.

Why moving a scale matters

This is the one people skip. A scale carries its calibration in the context of how it sits on the floor. Move it to a room with a different floor and the levelling changes; an unlevel scale reads consistently wrong, which looks exactly like a real weight change in a patient being monitored.

Re-level and re-zero after every move, and note it in the record.

What to record

• Date and who performed the check
• Instrument identifier — not "the scale in room 3"
• Result at each test point
• Action taken if out of tolerance
• Date of next scheduled calibration

Label each instrument with its last and next calibration date. Staff should be able to see at a glance whether the scale in front of them is in date.

When to retire

Retire a scale that cannot be brought back into tolerance, that fails to return to zero reliably, or whose readings vary between repeated weighings of the same load. Keeping a drifted scale "for rough weights" invites someone using it for a real one.

Replacements are in medical scales. See also approved-class scales.

This article is part of our guide to Medical Scales: Choosing the Right Scale for Your Practice.