Preset tare value
= Preset tare value
{title2=$\mathrm{PT}$}
A <preset tare value> is a numerical <tare mass> entered or recalled for use in subsequent weighings without individually determining each container's tare. The pinned OIML terminology denotes it by $\mathrm{PT}$ and calls the measured gross or net indication minus this value a <calculated net value>. It can be supplied through a <preset tare device> rather than obtained by weighing the current empty container.<Non-automatic weighing instruments, Part 1>[OIML R76-1:2006(E), T.2.7.5, printed page12; T.5.3.1–T.5.3.2, printed page16]{ref}
For an original example, a stored container tare is $\mathrm{PT}=250\,\mathrm g$, but the actual empty container has <tare mass> $T=263\,\mathrm g$. Adding $500\,\mathrm g$ of material gives <gross mass> $G=763\,\mathrm g$. Applying the stored value gives
$$
N_{\rm calc}=G-\mathrm{PT}=513\,\mathrm g,
$$
although the actual <net mass> is $N=G-T=500\,\mathrm g$. Their difference is
$$
\boxed{N_{\rm calc}-N=T-\mathrm{PT}=13\,\mathrm g.}
$$
An underestimated preset tare therefore overestimates the contents. Repeating the same discrepancy across ten containers produces a $130\,\mathrm g$ total discrepancy; more displayed digits do not remove it.
A useful physical check independently weighs representative empty containers, including the same lids and attachments used during the loaded measurement, and compares them with the stored value. Record which load components the preset represents. If it is subtracted from an indication that has already had those components removed by a <tare device>, the same <tare mass> is deducted twice. The stored number's provenance and variability belong in the <measurement model> and its <measurement uncertainty>.