On a breathalyzer spec sheet, ±0.005 %BAC looks small and clear, but taken on its own, it is a weak basis for comparison. %BAC is a percentage unit used to express blood alcohol concentration (BAC), and a breathalyzer displays the result of analyzing a breath sample in this and other units. An accuracy specification is information that explains how much difference a device shows under which conditions. It is not a rule for recalculating and correcting an individual reading shown on the screen.
When safety managers or quality and technical staff review the performance of several products, they should first read the reference concentration and temperature tied to the number, before the number after ±. DATECH's official product information for the AF-40BT gives the accuracy as ±0.005 %BAC and also states at 0.100 %BAC, 25 ℃. In this way, accuracy, display unit, reference concentration, and temperature must be compared together as one specification statement.
Read the accuracy figure within its test conditions
In ±0.005 %BAC, the ± value is the notation showing the range of difference in the accuracy specification. In the AF-40BT's published specification, however, this value is combined with at 0.100 %BAC, 25 ℃. 0.100 %BAC is the reference concentration at which the accuracy is stated, and 25 ℃ is the temperature condition attached to that figure.
So this statement alone does not let you say the same ± value applies across every concentration range or at every site temperature. Conversely, the mere fact that the site temperature differs from 25 ℃ does not let you conclude that performance has changed. The key is to separate the range the published specification directly explains from the range that requires additional data to judge.
Keep four items together as one set in the comparison table
If you copy only the number into a narrow column of a product comparison table, the reference conditions are easily lost. An accuracy specification must be recorded together with its original wording and conditions so you can later revisit the premises of the comparison. In particular, if you mix information from similar model names or updated product pages, the same figure may turn out to describe a different product.
| Comparison item | What to record with it | What to look at when comparing |
|---|---|---|
| Accuracy | ± value and display unit | Write the number and unit exactly as in the original. |
| Reference point | Reference concentration and temperature | Distinguish whether the two products' conditions are the same. |
| Product identification | Manufacturer name and model name | Do not mix in information about similar models. |
| Check history | Product page checked and when | Track whether the specification changes later. |
In addition to %BAC, the AF-40BT also lists ±0.05 ‰ (at 1.00 ‰, 25 ℃) and ±0.025 mg/L (at 0.50 mg/L, 25 ℃). This is why, even for several figures on the same page, you must not judge one as smaller or stricter just by looking at its digits. Each has a different display unit and a corresponding reference concentration, so you must first check whether the comparison units match.
When units differ, the size of the number is no basis for comparison
%BAC, ‰, and mg/L are different display units that can appear together on a spec sheet. So you cannot rank which specification is more accurate just by listing 0.005, 0.05, and 0.025. The moment a number is separated from its unit, its meaning changes.
There may be situations where you need to standardize on one unit in an internal system. In that case, it is appropriate to keep not only the converted management value but also the original specification statement and display unit given by the manufacturer. Keeping the original lets reviewers check what was carried over on what basis, and avoids confusing unit conversion with interpretation of the specification.
Steps to check in a hypothetical comparison
As a hypothetical case, suppose a purchase review table lists both Device A and Device B as ±0.005 %BAC. The first observation is only that the ± value and unit in the two entries are the same. At this stage, there is still no basis for interpreting the two devices' accuracy as having been stated under the same conditions.
Suppose at 0.100 %BAC, 25 ℃ is confirmed in A's official document, while B's document states no reference concentration or temperature. A possible action is to obtain B's official product information or additional data on the accuracy conditions linked to that product. The completion standard for the comparison is a state in which it has been confirmed whether the reference concentration and temperature of the two specifications are the same, or in which the table clearly records that B's conditions cannot be confirmed from published data.
In this case, the conclusion "B has lower performance" does not follow. The conclusion you can confirm is that, with the current data, you cannot compare whether the two numbers come from the same conditions. Leaving unconfirmed items blank or marked "conditions unconfirmed" shows the scope of the spec comparison more accurately than filling in estimated values.
Do not add or subtract the spec value from individual test results
An accuracy specification describes a device's declared performance. It is not a formula for correcting a single individual test result. For example, reinterpreting a result by subtracting or adding 0.005 %BAC to the displayed value is not something that can be derived from that specification wording. Using this number to judge whether an individual can drive is also outside the scope of the accuracy specification.
If you have doubts about a result itself, it is better to separate the handling of the individual result from a review of product performance. For product comparison, use official specifications that carry the reference concentration, temperature, and unit, and do not draw conclusions about performance at concentrations or in environments outside the reference point until relevant data has been confirmed. In the end, the reference point for properly comparing ±0.005 %BAC is not the ± value alone, but the whole statement, including the concentration and temperature at which that value is declared.
