This document discusses units and measurements in the International System of Units (SI) including base units, prefixes, and derived units. It provides examples of units used to measure length, area, volume, frequency, velocity, acceleration, force, pressure, work, energy, heat, power, mass, quantity, and concentration. Key units discussed include meters, liters, hertz, newtons, pascals, joules, watts, kilograms, grams, osmoles, daltons, and concentrations in grams per liter or grams per deciliter. The document concludes with medical examples applying these units such as blood pressure, pulse rate, and clinical measurements like hemoglobin and cholesterol levels.

1. Units and Measurements
& Basic Statistics
Prof Vajira Weerasinghe
Professor of Physiology

2. SI Units (introduced in 1960 in Europe)
Base Units

3. Multiples

4. Submultiples

5. Derived
Units

6. Rules
 Prefix attached to one unit: mg/l preferred to ug/ml
 Both formats acceptable: mg/l or mg l-1
 Ampere x second is written as A.s
 No space between prefix and unit : ms is millisecond

7. Length, area and volume
 Angstrom = 10-10
m
 Micron = 10-6
m
 Derived units
 Area = m2
 Volume = m3
= 1000 l
1 ml = 1 cm3
1 dl = 100 ml

8. Frequency, Velocity and
Acceleration
 Frequency is how often a periodic event occurs
 Hertz (Hz) or s-1
 Velocity is the distance per time:
ms-1
 Acceleration is the change of velocity
ms-2
 Negative value refers to deceleration

9. Force and Pressure
 Force is the acceleration times mass
kg ms-2
which is called 1 Newton (N)
 1 dyne = 10-5
N
 Pressure is force exerted on an area or Nm-2
 Unit is Pascal (Pa)
 1 mmHg = 0.133 Pa
 1 cmH2O = 98 Pa
 1 bar = 100 kPa

10. Work, Energy, Heat and Power
 Work is the force times distance (N x m)
 Unit joule (J)
 Energy and Unit have the same unit, the joule
 1 calorie = 4.185 J
 1 kilocalorie = 4.185 kJ
 Power is the work per time: J x s-1
= watt (W)

11. Mass, Quantity and Concentration
 Unit of mass is kg
 Quantity of a substance is the molecular weight expressed in grams or
gram molecular weight or mole
 Ions are expressed as equivalents (eq)
 Another derived unit is osmoles or Osmol
 Osmolarity of a solution is the concentration of osmotically active particles
 Unit = osml-1
 Osmolality is measured as osmkg-1
 Mass of a molecule or an atom is expressed as Dalton
 1 Dalton = 1.66 x 10-27
kg
 Concentration refers to
 Mass per volume gl-1
 g/dl or g/100 ml which is same as g%

12. Examples
 Blood pressure = 120/80 mmHg
 Pulse rate = 70 beats per min
 Red cell count = 5 million mm-3
or microlitre (10-6
l)
 Haemoglobin = 15 g/dl
 Mean Corpuscular Volume = 88 fl (femtolitre)
 Mean Corpuscular Haemoglobin = 30 pg (picograms)
 Fasting glucose = 100 mg/dl
 Total Cholesterol = 150 mg/dl
 Red cell count = mm-3