C z e c h  M e t r o l o g y  I n s t i t u t e  
Okružní 31,  638 00  
Brno  
 
1. ------IND- 2010 0774 CZ - EN- ------ 20101224 --- --- PROJET 
 
The Czech Metrology Institute (CMI), as the competent local body for stipulating metrological and 
technical requirements for a specified measuring device and for the stipulation of test method s for type 
approval and for verification of a specified measuring device pursuant to Section 14(1) of Act No. 
505/1990 Coll., on Metrology, as amended, and pursuant to provisions of Section 172 et seq. of Act 
No. 500/2004 Coll., the Administrative Code, as  amended (hereinafter the "AC"), has on 30 July 2010 
commenced ex officio proceedings pursuant to Section 46 of the AC, and based on su pporting doc u-
ments issues this:  
 
 
I. 
M E A S U R E  O F  A  G E N E R A L  N A T U R E  
number: 0111 -OOP -C016 -10 
reference  no. 0313/009/10/Pos.,  
publication date: 11 October 2010  
 
stipulating metrological and technical requirements for specified measuring devices, 
including test methods for verifying specified measuring devices:  
"laboratory lactometers with increments ≤  0,5 kg · m-3" 
 
1   Basic definitions  
For the purposes of this measure of a general nature, terminology and definitions contained in the 
VIM1) and the following apply:  
1.1   hydrometer with constant mass : a measuring device with constant mass w hose depth of imme r-
sion in the measured liquid determines its density or concentration of one of its comp onents  
NOTE   The hydrometer may or may not include a thermometer.  
1.2   laboratory lactometers with increments ≤  0,5 kg · m-3: a glass hydrometer with constant mass 
intended for the measurement of the density of milk and liquid milk products under laboratory cond i-
tions  
2   Metrological requirements  
2.1   Stipulated service conditions  
A lactometer must meet metrological requirements for service temperatur e range specified by the 
manufacturer. If the manufacturer does not specify this, a service temperature range of +10  °C to 
+30 °C applies.  
                                                      
1)   International Vocabulary of Metrology - Basic and General Concepts and Associated Terms (VIM).  Measure of a General Nature No. 0111 -OOP -C016-10 
2 The reference temperature for testing lactometers is 20  °C, reference pressure is normal atmospheric 
pressure.  
2.2   Measurement range  
The measurement interval of a laboratory lactometer is specified by the manufacturer. If it is not spec i-
fied by the manufacturer, a measurement interval of 1015  kg · m-3 to 1025  kg · m-3 or from 
1025  kg · m-3 to 1 035 kg · m-3 applies.  
If the laboratory lactometer includes a thermometer, its measurement interval must correspond to the 
service temperatures specified in Article 2.1.  
2.3   Maximum permissible error  
2.3.1    Maximum permissible lactometer error  
The maximum permissible error of a laboratory lactometer is ±  0.2 kg · m-3 for lactometers with i n-
crements of 0.2  kg · m-3 and ±  0.25 kg · m-3 for lactometers with increments of 0.5  kg · m-3. 
2.3.2    Maximum permissible thermometer error  
The maximum permissible error of a thermometer that  is part of a lactometer is ±  0,5 °C. 
3   Technical requirements  
3.1   Lactometer design  
A laboratory lactometer is composed of a glass tube, which may have a built -in thermometer, and 
whose lower portion contains a conical or hemispherical weight. Connect ed to the upper part is a c y-
lindrical stem that is sealed at its upper end.  
The entire outside surface of the lactometer must be symmetrical around its main axis. A circular 
cross -section must not exhibit any sudden changes, and transitions of all parts of  the lactometer must 
be smooth and rounded.  
The taper ratio of the stem must not exceed 0.1 mm per 100 mm. The maximum permissible deviation 
from circularity of any stem cross -section along the entire length of the scale is 0.10 mm.  
The entire length of th e lactometer must not exceed 350 mm.  
No part of the lactometer may contain any unattached material.  
3.2   Lactometer graduated scale  
A lactometer may have only one graduated scale, which must fit tightly against the inside wall of the 
lactometer casing, mu st not exhibit unevenness and must not be helically twisted. The graduated scale 
of the lactometer must not have been damaged by flame during sealing of the stem.  
The graduated scale markings must be perpendicular to the axis of the lactometer, parallel to  each 
other, and clear. All lactometer graduated scale markings must have the same thickness, which must 
be no more than 0.2 mm.  
If lactometer graduated scale markings have differing lengths, then the length of short markings must 
be at least one fifth of the circumference of the stem, medium markings at least one third of the ci r-
cumference of the stem, and long markings at least half of the circumference of the stem. All grad u-
ated scale markings must be right -aligned along one imaginary perpendicular line.  
The entire length of the graduated scale must be (83  ± 10) mm for lactometers with increments of 
0.2 kg · m-3 and (55  ± 7) mm for lactometers with increments of 0.5  kg · m-3. Measure of a G eneral Nature No. 0111 -OOP -C016-10 
3 The highest graduated scale marking on the lactometer must be at least 15 mm bel ow the top of the 
stem, and the lowest marking at least 5 mm above the location where the stem widens to meet the cy l-
inder.  
Lactometers are calibrated to be read at the lowest part of the meniscus.  
To check that the lactometer graduated scale is correctly located in the stem, the stem surface must 
have a verification line that aligns with the highest numbered mark on the graduated scale.  
The mutual positioning of the lactometer graduated scale and thermometer must be such that the va l-
ues of both graduated s cales can be read without turning the lactometer, and the right ends of the la c-
tometer graduated scale lines must pass behind the profile of the stem.  
3.3    Lactometer thermometer  
The capillary must be capable of withstanding an upper temperature limit of  +50 °C or the upper limit 
of the upper measurement limit of the thermometer's graduated scale in accordance with  Article 2.2 
plus 10  °C, whichever is greater.  
The divisions of the thermometer's graduated scale must be 0.5 C.  
The total length of the thermo meter's graduated scale must be at least 40 mm.  
To check that the thermometer's graduated scale is attached correctly, a verification line is placed on 
the backside of the cylinder at the location of the reference temperature marking during lactometer 
calibration.  
3.4   Working position of the lactometer  
The lactometer must float in liquid with its vertical axis perpendicular to the surface. The deviation of 
the lactometer's axis to the side from vertical when looking at the lactometer's graduated scale mus t 
not be greater than 1º 30´.  
When meeting the previous requirement, stability must also be maintained, where the lactometer is 
deflected to the opposite side and then must return to its original position.  
3.5   Material  
The glass used in the manufacture o f lactometers must be transparent, colourless and must permit easy 
reading of the graduated scale.  
4   Markings  
4.1   Markings on the measuring device  
A laboratory lactometer must be legibly and permanently marked with the following information:  
– the manufa cturer's name or mark,  
– measuring device type,  
– serial number and date of manufacture,  
– unit of measurement (kg  · m-3), 
– reference temperature (20  °C), 
– the type of liquid for which the hydrometer is intended, e.g. milk,  
– how to read data (read at lowest point o f meniscus),  
– type approval mark.  Measure of a General Nature No. 0111 -OOP -C016-10 
4 4.2   Verification marks  
The verification mark is etched onto the backside of the body of the alcoholmeter below the stem a t-
tachment location. After a lactometer is verified, a verification certificate may be issued upon th e 
user's request, listing the test temperature and liquid used and how data was read.  
5   Type approval  
5.1   In general  
The approval process for the measuring device includes the following tests:  
a) external inspection,  
b) shape and dimension check,  
c) test for st ability and to ensure that the axis of the stem of the lactometer is perpendicular to the 
surface of the liquid in which it is floating,  
d) lactometer accuracy test,  
e) thermometer accuracy test.  
5.2   External inspection  
The following is assessed during an exte rnal inspection:  
a) that prescribed tec hnical documentation is complete, including the user manual,  
b) that metrological and technical characteristics specified by the manufacturer in documentation 
conform to requirements of this regulation listed in sections 2 and 3,  
c) the appearance and completeness of information in accordance with  prescribed technical 
document ation. 
5.3   Lactometer shape and dimension check  
The shape and surface of the lactometer must not exhibit any sudden changes and transitions.  
The deviati on from circularity and the taper of the lactometer stem are checked at each marked point 
of the lactometer's graduated scale with a micrometer to an accuracy of ±  0.01 mm, and the devi ation 
from circularity of any stem cross -section must not exceed values  listed in Article 3.1.  
The total length of the lactometer is measured with a length measurement device with an accuracy of 
± 0.5 mm. 
The prescribed dimensions of the lactometer's graduated scale markings are checked with a length 
measurement device to an accuracy of 0.01 mm.  
5.4   Functional tests  
5.4.1    Calibration solutions  
Calibration liquids are solutions of  
– 96% wt. sulphuric acid and 80% wt. finely refined alcohol, or  
– sodium carbonate and finely refined alcohol.  
Prior to testing, solutions must be t empered to laboratory temperature with a maximum deviation of 
± 5 °C from the reference temperature, and temperature changes during measurement must not exceed 
± 0.5 °C · h-1. Measure of a G eneral Nature No. 0111 -OOP -C016-10 
5 5.4.2    Test for stability and to ensure that the axis of the stem of the lactom eter is perpendicular 
to the su rface of the liquid in which it is floating  
The perpendicularity of the stem axis is tested by submerging the lactometer into a suitable calibr ation 
liquid up to the lower edge of the lactometer's graduated scale. Using an an gle template placed behind 
the lactometer, the deviations of the lactometer's stem from vertical is determined. The projection of 
the outline of the stem is observed from a distance of at least 250 mm.  
The subsequent stability test is performed by tilting the lactometer opposite to its stem's lean angle.  
This test must meet the requirements of Article 3.4.  
5.4.3    Lactometer accuracy test  
Prior to the test, the lactometer and all necessary aids must be thoroughly degreased by dipping into 
chromic sulphuric acid for at least 30 minutes, rinsing with running water and rinsing with distilled 
water.  
Accuracy is tested by comparing measured values of the tested lactometer against the values of a re f-
erence lactometer in calibration liquids for the given lactometer  measurement interval in accordance 
with Article 5.4.1.  
Measurement is performed at least three times for at least five points of the graduated scale.  
During the test, it is important to ensure that the lactometer and thermometer (that is part of the test 
bath) are at least 10 mm apart and away from the walls of the container with the calibration liquid.  
After the test, both the reference and tested lactometers are rinsed with petroleum ether.  
The measurement error at each point of the graduated scale must not exceed the maximum permissible 
error in accordance with  Article 2.3.1.  
5.4.4    Lactometer thermometer accuracy test  
The accuracy of the thermometer (that is part of the lactometer) is tested by comparing measured va l-
ues of the tested thermometer with v alues of a reference thermometer, for at least three points of the 
scale: at the alcoholmeter's reference temperature and at both endpoints of the thermometer's scale.  
The measurement error at each point of the graduated scale must not exceed the maximum p ermissible 
error in accordance with  Article 2.3.2.  
6   Initial verification  
6.1   In general  
The following is performed during initial verification:  
a) external inspection,  
b) shape and dimension check,  
c) test for stability and to ensure that the axis of the stem of the lactometer is perpendicular 
to the surface of the liquid in which it is floating,  
d) lactometer accuracy test,  
e) thermometer accuracy test.  
6.2   Visual inspection  
The following is assessed during visual inspection of laboratory lactometers:  
a) that the mea suring device is the same as the approved type;  
b) appearance (including description) and condition of the measuring device.  Measure of a General Nature No. 0111 -OOP -C016-10 
6 6.3   Lactometer shape and dimension check  
Shape and dimensions of the lactometer are checked in accordance with  Article 5.3.  
6.4   Functional tests  
6.4.1    Test for stability and to ensure that the axis of the stem of the lactometer is perpendicular 
to the su rface of the liquid in which it is floating  
The test for stability and to ensure that the axis of the stem of the lactometer is pe rpendicular to the 
surface of the liquid in which it is floating is performed in accordance with  Article 5.4.2.  
6.4.2    Lactometer accuracy test  
The lactometer accuracy test is performed in accordance with  Article 5.4.3.  
6.4.3    Lactometer thermometer accu racy test  
The accuracy test of the thermometer as part of the lactometer is performed in accordance with  Article 
5.4.4.  
7   Subsequent verification  
These measuring devices are not subject to subsequent verification.  
8   Notified standards  
To specify metrol ogical and technical requirements for measuring devices and to specify verific ation 
test methods stemming from this measure of a general nature, the CMI notifies Czech technical sta n-
dards, other technical standards or technical documents of international o r foreign organizations or 
other technical documents containing detailed technical requirements (hereinafter "notified sta n-
dards"). The CMI shall publish a list of these notified standards, with their assignation to relevant 
measures, along with the measur e of a general nature, in a manner available to the public (on the we b-
site www.cmi.cz).  
Compliance with notified standards or parts thereof is considered to be, to the extent and under the 
conditions stipulated by a measure of a general nature, to be compl iance with those requirements 
stipulated by this measure to which these standards or parts thereof apply.  
 
 
II. 
J U S T I F I C A T I O N  
The CMI issues, towards the implementation of Section 24c of Act No. 505/1990 Coll., on metrology, 
as amended, this me asure of a general nature, stipulating metrological and technical requirements for 
specified measuring devices and test methods for verification of these specified measuring devices.  
In Decree No. 345/2002 Coll., specif ying measuring devices for mandatory verification and measuring 
devices subject to type approval, as amended, the annex "List of Specified Measuring Device Types" 
classifies " laboratory lactometers with increments  ≤  0,5 kg · m-3" under item 7.1.5 as measuring d e-
vices subject to type approval  and verific ation. 
The CMI thus issues, towards the implementation of Section 24c of Act No. 505/1990 Coll., on m e-
trology, as amended, for the measuring device type specified as " laboratory lactometers with incr e-
ments ≤  0,5 kg · m-3", this measure of a gen eral nature, stipulating metrological and technical requir e-
ments for  laboratory lactometers with increments  ≤  0,5 kg · m-3 and test methods for type a pproval 
and verification of these specified measuring d evices.  Measure of a G eneral Nature No. 0111 -OOP -C016-10 
7  
 
III. 
N O T I C E  
A measure of a general nature cannot be appealed (Section 173 (2) of Act No. 500/2004 Coll., the 
Administrative Code, as amended (hereinafter the "Administrative Code").  
Pursuant to provisions of Section 172 (5) of the Administrative Code, a decision on objections cannot 
be appe aled in any manner.  
The conformance of a measure of a general nature with legislation can be assessed in review procee d-
ings pursuant to Section 94 to 96 of the Administrative Code. A participant may submit a request for a 
review to the administrative body that issued this measure of a general nature. If the administrative 
body does not find reasons for commencing review pr oceedings, it shall notify the applicant within 
thirty days of this fact along with its reasons. A decision on commencement of review proceedings 
can, in accordance with  Section 174 (2) of the Administrative Code, be issued within three years of the 
effective date of the measure of a general nature.  
 
 
 
IV. 
E F F E C T I V E  D  A T E  
This measure of a general nature takes effect on the fifteenth day following the day of its publication 
(Section 24d of Act No. 505/1990 Coll., on metrology, as amended).  
This m easure of a general nature shall be published for a period of 15 days.