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Gray Morris
Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
Unit One: Chapter 1
Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
3Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
After reviewing this chapter, you should be able to:
› Recognize the symbols used to represent numbers in the Roman numeral system
› Convert Roman numerals to Arabic numbers
› Convert Arabic numbers to Roman numerals
4Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
History Application in apothecary system
› Grains (gr) combined with Roman numerals› x = 10 in Roman numeral expressions
Note: “gr” precedes the number in Apothecary system
x 10 gr grains
5Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
Roman numerals and time pieces
6Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
May still see in practice› Aspirin gr x = Aspirin 10 grains
Knowing values helps prevent errors
Safety Tip The Institute for Safe Medication Practice (ISMP) at www.ismp.org
› Recommendation: abbreviations and med errors
7Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
Arabic system—numbers› Numbers not letters (1, 2, 3…)› Fractions (¼, ¾)› Decimals (0.5, 1.2)
Roman Numerals—letters› i, v, x used most often› Line may be used to prevent
interpretation error
i, vii, ix
8Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
9Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
1. When a Roman numeral of lesser value is placed AFTER one of equal value, the numerals are added25 = xxv (x = 10 x = 10 , v = 5 10+10+5
= 25)
2. Same numeral is never repeated more than three times
4 = iv NOT iiii
10Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
3. When a Roman numeral of lesser value is placed BEFORE a numeral of greater value, the numbers are subtracted
ix = 9 (x = 10, i = 1 10 - 1 = 9)
xxiv = 24 (x = 10 + x = 10 + iv = [5 – 1] = 24)