A NEW MS EXCEL ADD-IN FOR ROUNDING
The rounding rules for calibration and testing results are established in the ISO 31-0,
“Quantities and Units - Part 0: General Principles.” This standard states that if you want
to round a number, you need first to look at the digit to the right side of the rounding
digit. This digit will be referred as the ‘dropped digit’.
If the dropped digit is less than or equal to four, you do not change the rounding digit;
that means you should round down. If the dropped digit is greater than five, the
rounding digit is increased by one number (i.e., rounded up).
The problem appears when the dropped digit is exactly five (or five followed only by
zeros). In this case, ISO 31-0 requires that you round down if the preceding digit is even
and round up if the preceding digit is odd (i.e., round off to the nearest even digit). This
rule is known as the ‘banker’s rounding’. For example: if you want to round off 0.45 to
the nearest tenth, you will get 0.4 (since four is even, you round down). On the other
hand, if you want to round off 0.75 to the nearest tenth, you will get 0.8 (since seven is
odd, you round up).
Unfortunately, the most popular spreadsheet software – MS EXCEL – does not perform
the banker’s rounding. Instead, when the dropped digit is exactly five, the MS EXCEL
rounding function (ROUND) will always round up (0.45 to 0.5 and 0.75 to 0.8). This
procedure adopted by MS EXCEL can introduce a systematic error and, thus, should be
avoided by calibration and testing laboratories.
The good news is that the Brazilian metrologist, Daniel Jornada, came up with a solution
to this issue. His consultancy company – Certificar – has developed a new function that
runs as a simple MS EXCEL add-in. The function – named LabRound – is freely available.
Instructions for downloading and installing this function are available at
http://sites.portalcertificar.com.br/rounding.
After installing, LabRound works in the same way as any MS EXCEL function. For
example, if you want to round off 0.45 to the nearest tenth, you just have to type in a
cell =LabRound(0.45;1). The ‘1’ refers to the number of decimals places to be
considered in the rounding.
Another advantage of this new function is related to rounding numbers that then end
with a zero. For example, if you try to round 0.303 to the nearest hundredth with MS
EXCEL rounding function, the result would be 0.3 (i.e., the last zero is not shown).
However, if you round with the LabRound function, the result would be 0.30,
maintaining the hundredth digit.
CERTIFICAR GESTÃO EMPRESARIAL S.S. LTDA.
Porto Alegre / RS: 51 3379.0480
Rio de Janeiro / RJ: 21 3717.5965
www.portalcertificar.com.br - [email protected]