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An additive tare device is a tare device that can establish a zero indication with a load present without reducing the weighing range available for net loads.^[ref] The supported container still contributes tare mass; the instrument provides a separate tare allowance rather than obtaining extra capacity simply by changing a displayed number.

Consider a deliberately specified model with maximum weighing capacity $\mathrm{Max}=5\mathrm{kg}$ for net loads and a maximum additive tare allowance $T_{\mathrm{add}}=2\mathrm{kg}$. Assume these ranges are available together for the stated configuration:A container with tare mass $T=1.2\mathrm{kg}$ can then accompany net mass $N=5\mathrm{kg}$, giving gross mass $G=6.2\mathrm{kg}$. The model's full combined boundary is $7\mathrm{kg}$ when both allowances are used. These numbers are chosen examples, not specifications for a particular scale.

By comparison, a subtractive tare device with a $5\mathrm{kg}$ gross-load budget would leave only $3.8\mathrm{kg}$ for net mass after the same $1.2\mathrm{kg}$ container is tared. Both displays can initially read zero; their available net-load capacities differ.

The OIML definition of maximum weighing capacity explicitly omits additive tare capacity, while its maximum-tare-effect terminology records the tare device's capacity separately.^[ref] A complete load description therefore identifies the container's tare mass, the desired net mass and the instrument's declared tare allowance. The load receptor continues to carry their combined physical load.

Gross mass is the mass of the complete specified load, including its contents and the packaging counted as tare mass. For that same boundary,The gross indication in OIML's weighing terminology is obtained with neither a tare device nor a preset tare device operating, after an initial zero indication.^[ref] A full crate's gross mass consequently differs from an individual jar's gross mass, because the specified loads differ.

Consider four jars, each containing $0.50\mathrm{kg}$ of material and having an empty-container tare mass of $0.20\mathrm{kg}$. An outer crate adds $0.80\mathrm{kg}$. For the complete load, the net mass of the contents, composite tare mass, and gross mass are respectivelyThese are chosen bookkeeping values, assuming the listed components exhaust the load and each component is counted once.

Subtracting the full composite tare mass from the complete gross mass gives $3.60-1.60=2.00\mathrm{kg}$ of contents. If the jars' $0.80\mathrm{kg}$ has already been removed from an intermediate total, subtracting the same full composite tare mass again gives $1.20\mathrm{kg}$. The missing $0.80\mathrm{kg}$ is precisely the duplicated deduction. Use one load boundary and subtract each packaging component once.

The gross mass also remains relevant to maximum weighing capacity when a subtractive tare device reduces the available net-load range.^[ref] For an illustrative instrument modeled with a $1.000\mathrm{kg}$ gross-load limit, a $0.120\mathrm{kg}$ container leaves $0.880\mathrm{kg}$ for contents. At that limit the complete load still has gross mass $1.000\mathrm{kg}$, even though the tared display reports only its contents.

For a stationary ideal weighing scale, the normal contact force associated with a complete load is related to its gravitational weight. A displayed net mass is a processed indication of that load; it is not the full supported mass. Changes in the gravitational field, measurement calibration, or the load boundary must therefore be distinguished when interpreting a reading.

The maximum weighing capacity, conventionally $\mathrm{Max}$, specifies the upper capacity of a weighing scale; the OIML definition excludes additional capacity provided by an additive tare device.^[ref] A display reset does not by itself establish a new physical load capacity.

For a chosen model with a subtractive tare device, let $\mathrm{Max}=5\mathrm{kg}$ and suppose the combined gross mass on the load receptor must satisfyA container with tare mass $1.2\mathrm{kg}$ leaves at most $3.8\mathrm{kg}$ for net mass. Pressing the tare device can make the display read zero with that container present, but the container remains part of the supported mass. This calculation assumes the stated subtractive-tare model; it does not assign the same capacity budget to a scale with an additive tare device.

The maximum safe load describes a different boundary: the static load an instrument can carry without permanently changing its metrological qualities. It does not define the upper end of its specified weighing capacity.^[ref] For example, an instrument could have a declared $\mathrm{Max}$ of $5\mathrm{kg}$ and a separately declared maximum safe load of $7\mathrm{kg}$. Those hypothetical markings would not turn a $6\mathrm{kg}$ indication into a measurement within the declared $5\mathrm{kg}$ weighing capacity.

A tare device establishes a zero indication on a weighing scale while a load remains on its load receptor. An additive tare device preserves the weighing range for net loads; a subtractive tare device reduces that range.^[ref]

For example, place an empty $0.40\mathrm{kg}$ container on the load receptor and operate the tare device. The display reads zero even though the scale still supports the container. Adding $1.10\mathrm{kg}$ of material gives gross mass $1.50\mathrm{kg}$ and, ideally, an indicated net mass of $1.10\mathrm{kg}$. Removing both material and container without clearing the tare would ideally give $-0.40\mathrm{kg}$. This negative indication is consistent with the changed reference.

The cancellation can be seen in a linear model. If the unrounded indication before tare is $r(m)=am+b$, and the supported container has tare mass $T$, the indicated result after adding net mass $N$ isThe additive offset $b$ and the container contribution cancel. A response scale factor $a\ne 1$ remains, so taring alone does not establish calibration across the load range.

The container's physical load remains on the scale after taring. Consequently the available maximum weighing capacity depends on the kind of tare device, even when two instruments show the same zero. A preset tare device performs a related numerical subtraction using an entered or recalled value, rather than necessarily measuring this particular empty container.