Written and maintained by CASRAI Editorial Board
Last updated
This page describes products and general use; it is not medical advice.
Who uses it: clinic and exam-room staff who weigh patients, buyers comparing models, and students learning how clinical weighing equipment works. After reading, you should be able to read a beam scale correctly, run its zero check, and make sense of the capacity and type-evaluation figures on a scale’s paperwork.
What a physician scale is
A physician scale is a platform scale built for weighing patients in a clinic or exam room, often with a height rod attached. One manufacturer describes its mechanical beam model as providing “a rugged mechanical design to measure patient weight and height.” Digital models exist too: a United States type-evaluation certificate for one electronic medical scale describes it as a “non-computing digital electronic scale designed for use in the medical field for weight assessment of ambulatory patients.”
Infant weighing and length measurement are separate product classes; see infant scales and the stadiometer guide.
How a mechanical beam physician scale is built
The example instructions for use (Henry Schein item 112-7157) name these parts: a scale platform, a pillar, two poise bars (the upper bar carries the large poise, the lower bar the small poise), a beam pointer that moves inside a trig-loop, a balance ball screw at the left end of the bar, a height rod with a headpiece, and a wheel bracket. The patient stands on the platform, and the poise weights are slid along the bars until the pointer sits centred in the trig-loop.
Types and variants
| Type | Typical use | Key difference |
|---|---|---|
| Mechanical beam scale with height rod | Weight and height of patients | Weight is found by balancing two sliding poise weights against a pointer; the reading is taken by hand (Henry Schein instructions, item 112-7157). |
| Digital (electronic) medical scale | Weight assessment of ambulatory patients | Electronic display; the example certificate lists an LCD, semi-automatic zero, automatic zero tracking, semi-automatic tare, a kg/lb key and a low-battery indicator (NTEP certificate 18-011). |
Digital medical scale
The example digital model’s certificate lists optional Bluetooth, and it carries a specific note: its body mass index (BMI) function “is not legal for trade (not NTEP tested).”
Medical scale with height
The example beam scale measures height with a rod and headpiece. Its instructions state that a patient must be at least 23 5/8 in (600 mm) tall for height to be measured accurately, and the height rod length listed is 200 cm.
Specifications that matter
| Specification | Mechanical beam example | Digital example |
|---|---|---|
| Capacity | 450 lb / 210 kg | 550 lb / 250 kg |
| Accuracy class (as listed) | Not listed | Class III |
| nmax (as listed) | Not listed | 2750 / 2500 |
| emin (as listed) | Not listed | 0.2 lb / 0.1 kg |
| Operating temperature (as listed) | Not listed | 5 to 35 °C (41 to 95 °F) |
| Height rod | 200 cm | Not listed |
These are single-model examples, not class definitions. Sources: the Henry Schein instructions for use for item 112-7157, and NTEP Certificate of Conformance 18-011 for Rice Lake Weighing Systems models 160-10-7N, 7NBT and 7NBLE (issued February 6, 2018). The certificate states the device was evaluated under the National Type Evaluation Program and found to comply with the applicable requirements of NIST Handbook 44. The certificate also notes that the National Conference on Weights and Measures does not approve or endorse any product.
How to choose: what the sources say to check
- Capacity. The beam instructions say “Do not exceed recommended weight limit of 450 lb / 210 kg.” Capacity is stated in pounds and kilograms; for weight-capacity planning in a clinic, see the bariatric clinic supply checklist.
- Stated application. The digital certificate states the scale is designed for weight assessment of ambulatory patients.
- Type-evaluation paperwork. A certificate names which functions were evaluated. In the example, BMI was not.
- Units. Both examples report pounds and kilograms (poise bar graduations on the beam scale; a kg/lb key on the digital scale).
Zero check and reading the beam
The instructions for use say the scale should be checked periodically, “particularly when moved.”
- Place the scale on a hard, flat, level surface and step on and off several times to settle internal parts.
- Set both poise weights to “0”. The beam pointer should float gently up and down and not touch the top or bottom of the trig-loop.
- If it is not centred, turn the balance ball screw (a flat-head screwdriver is required).
To weigh: set the poises near the expected weight, step on, and move them until the pointer is centred. You need not wait for it to stop, as long as it moves equally within the trig-loop opening. Read the value nearest the indicator arrow on each poise and add the two. Pounds are the silver graduations on black on the upper part of each bar; kilograms are black on silver on the lower part. Worked example from the instructions: large poise at 400 lb plus small poise at 41 lb gives 441 lb.
For background on how a scale differs from a balance, see scale vs balance.
Safe use, cleaning and service
- Use on a flat, stable surface; do not drop the scale or subject it to violent shocks.
- If the scale is damaged, do not operate it until properly serviced; repairs only by a qualified service agent.
- Clean external surfaces with a damp cloth or mild antimicrobial soap and water, then dry. Do not immerse the scale. Do not use abrasive or acid cleaners, white spirit or benzene.
- Service: for this model the manufacturer recommends service by a qualified service lab every 3 to 5 years, depending on frequency of use.
Common mistakes and troubleshooting
| Symptom | Cause given by the manufacturer | Action given |
|---|---|---|
| Pointer not centred at “0” | Bar does not “0” balance | Seat both poises firmly against the beam shoulder; adjust the balance ball screw at the left end of the bar. |
| Bar does not move freely | Bar sticking or adjustment needed | Check whether the pointer touches the side of the trig-loop; the beam may need realignment. |
| Platform rocks or touches the base at a corner | Base out of alignment | Contact technical support. |
| Beam does not move during weighing | Improper steel rod connection, or a poise set higher than the patient’s weight | Reset to a lower weight; check the rod connection. |
For other weighing and laboratory instruments, see the lab equipment hub. Clinic diagnostic equipment is also grouped under diagnostic, monitoring and imaging supplies.
FAQ
What is a medical scale?
A scale designed for weighing patients. Manufacturer documents describe a mechanical beam scale that measures patient weight and height, and a digital scale designed for weight assessment of ambulatory patients.
What is the difference between a beam and a digital medical scale?
A beam scale is read by balancing sliding poise weights against a pointer and adding two readings. The digital example shows weight on an LCD and lists features such as automatic zero tracking and a kg/lb key.
Does a medical scale need calibration?
The beam model’s instructions call for a periodic zero check, particularly after moving it, and recommend professional service every 3 to 5 years depending on use. Requirements for other scales come from their own manufacturer’s instructions.
What does Class III mean on a certificate?
It is the “Accuracy Class” printed on the example digital scale’s NTEP certificate, alongside capacity, nmax and emin. The certificate records the evaluation under NIST Handbook 44; read the certificate for the model you are considering.
Is the BMI function on a digital scale legal for trade?
On the example certificate, no: it states BMI “is not legal for trade (not NTEP tested).”
Sources
- Henry Schein, Mechanical Beam Scale with Height Rod, item 112-7157, user instructions: henryschein.com/assets/Medical/HS1127157.pdf (checked 2026-10-30).
- NCWM National Type Evaluation Program, Certificate of Conformance 18-011, Rice Lake Weighing Systems: ricelake.com NTEP 18-011 (PDF) (issued February 6, 2018; checked 2026-10-30).
