Internal vs External Calibration Balances: A&D FZ-120i vs FX-120i Explained
Internal vs external calibration balance: the A&D FZ-120i calibrates itself with a built-in weight for $819.00, and the A&D FX-120i reads the same 0.001 g with an external weight for $699.00; both are in stock.
Short answer: an internal calibration balance has a built-in weight, so you calibrate it by pressing a key (or it calibrates itself automatically) instead of placing a certified weight on the pan. An external calibration balance needs a separate calibration weight, not included, but costs less. The A&D FZ-120i (internal, one-touch) and the A&D FX-120i (external) weigh the same 122 g x 0.001 g, so the choice comes down to how often your room temperature changes, how often you move the balance, and whether you need calibration records.
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“Should I pay more for internal calibration?” is one of the most common questions we get from lab, pharmacy and reloading customers. MNM Scales is an authorized A&D dealer and one of the largest scale distributors in the country, with over 30 years in business and the largest selection of internal and external calibration balances. Here is what the extra cost buys you.
Why balances need calibrating at all
A balance measures force and converts it to mass, and its sensitivity shifts slightly with temperature, location and time. A&D rates the FX-i and FZ-i sensors at ±2 ppm/°C sensitivity drift. If the room warms by 5 °C, that is 10 ppm, or about 0.001 g on a 100 g load: one full division on a 1 mg balance. Calibration (strictly, adjustment) resets the sensitivity against a known mass so the reading is right again. How you supply that known mass is the difference between internal and external calibration.
Three ways a balance calibrates
- External calibration: you place a certified weight of the right value and class on the pan when the balance asks for it. Examples: FX-120i, FX-300i, FX-3000i and the FX-104 analytical balance. The weight is not included unless the listing says so (the FX-300i listing includes a free 100 g weight).
- One-touch internal calibration: press CAL and the balance lowers its built-in mass, calibrates and returns to weighing. On the FZ-120i and FZ-300i, A&D drives the internal mass with an air pump, and the FZ-i adds a clock and calendar so the GLP calibration report carries the date and time.
- Automatic internal calibration: the balance calibrates itself. The A&D GX-1003A and other GX-A Apollo models can be set to calibrate when the temperature changes, at an interval of 0.5 to 24 hours, or at up to three set times a day; keep the pan clear (under 2 g on 0.001 g models) so it can run. Sartorius isoCAL works the same way (see Sartorius Entris II compared).
FZ-120i vs FX-120i: same weighing, different calibration
| A&D FX-120i | A&D FZ-120i | |
|---|---|---|
| Capacity x readability | 122 g x 0.001 g | 122 g x 0.001 g |
| Repeatability / linearity | 0.001 g / ±0.002 g | 0.001 g / ±0.002 g |
| Stabilization | About 1 s (FAST) | About 1 s (FAST) |
| Calibration | External: 100 g or 50 g weight, not included | Internal one-touch, plus external |
| Clock and calendar | No | Yes, for dated GLP reports |
| Net weight | About 2.5 kg | About 3.0 kg |
| MNM price | $699 | $819 |
Add a 100 g A&D calibration weight ($59) to the FX-120i and the gap is about $60. The same comparison holds one size up: the FX-300i ($659, free 100 g weight included) and the FZ-300i ($829), both 320 g x 0.001 g. For the full FX family, see FX-120i vs FX-120iN vs FX-300i.
Internal calibration still needs an outside check
A built-in weight is not checked by anyone unless you check it. A&D notes that the internal mass can change over time from corrosion, damage or aging, and recommends checking it periodically with an external weight; the FZ-120i through FZ-500i can correct the internal mass value by up to ±0.050 g against a 100 g or 200 g reference. OHAUS builds the same check into the Pioneer PX: on the PX124 you weigh a test weight after an internal calibration and correct any offset under InCal Adjust (see our OHAUS PX124 manual guide). That is why labs keep a certified check weight even with internal calibration (see calibration weight classes and calibration weights), and why audits ask for a periodic calibration certificate from an outside provider (see NIST-traceable vs in-house certificates and how often to calibrate).
Which should you buy?
- Choose external calibration when the balance stays in one place at a steady room temperature and you are comfortable handling a weight, for example reloading benches (see our reloading scale guide and FX-120i AutoTrickler setup). Calibration takes a minute; see how to calibrate the FX-120i.
- Choose one-touch internal calibration (FZ-i) when several people use the balance, it gets moved, or the room temperature swings during the day, and you want dated calibration reports without buying a weight.
- Choose automatic internal calibration (GX-A, Sartorius isoCAL) for regulated labs and pharmacies that need the balance kept in adjustment without anyone remembering to do it (see our pharmacy balance guide). At 0.1 mg, the GX-124AN adds NTEP approval; compare it with the external-calibration FX-104 in analytical vs precision balances.
- Selling by weight? Pick an NTEP model such as the FX-120iN (see what NTEP means).
Calibration service and certificates
Whichever type you choose, we can calibrate it before it ships or after you send it in, with an in-house or NIST-traceable certificate. Pricing follows maximum capacity (see calibration pricing):
Up to 2.2 kg (FX-120i, FZ-120i, FX-300i, FZ-300i, GX-1003A, FX-104, GX-124AN): In-house calibration + certificate ($95) NIST calibration + NIST-traceable certificate ($395)
Over 2.2 to 6.2 kg (FX-3000i): In-house calibration + certificate ($195) NIST calibration + NIST-traceable certificate ($495)
Frequently asked questions
What is an internal calibration balance?
An internal calibration balance has a built-in calibration weight. You calibrate it by pressing a key, or it calibrates itself automatically, without placing a separate weight on the pan.
What is the difference between the A&D FZ-120i and FX-120i?
Both weigh 122 g x 0.001 g with the same repeatability and linearity. The FZ-120i has one-touch internal calibration and a clock and calendar; the FX-120i uses an external calibration weight, not included, and costs less.
Does the FZ-120i calibrate itself automatically?
The FZ-120i calibrates with its internal mass when you press the CAL key. Automatic self calibration on temperature change or a set time is a feature of models such as the A&D GX-A series and Sartorius isoCAL balances.
Do I still need a calibration weight with internal calibration?
It is good practice. The internal mass can change over time, so A&D recommends checking it periodically with an external weight, and audits usually require a periodic outside calibration certificate.
What calibration weight does the FX-120i need?
The FX-120i calibrates with a 100 g or 50 g weight, not included. MNM Scales sells a 100 g A&D calibration weight for the FX-120i.
How much does it cost to calibrate an FZ-120i or FX-120i?
At MNM Scales, balances up to 2.2 kg cost $95 for in-house calibration with a certificate or $395 for NIST calibration with a NIST-traceable certificate.