Roman Numerals and Military Time
Upon completion of this chapter, the learner will be able to:
1. Define the key terms that relate to Roman numerals and military time.
2. Demonstrate how to convert Arabic numerals into Roman numerals with 100% accuracy.
3. Convert times from a 12-hour clock to a 24-hour clock, and vice versa, with 100% accuracy.
4. Demonstrate proper strategies for rounding numbers.
5. Compute problems that ask for rounding of numbers with 100% accuracy.
6. Apply functional knowledge of a scientific calculator to solve problems with 100% accuracy.
The number system used in the Western Hemisphere, related to the English system of measurement.
Time based on a 24-hour clock.
Letter symbols used by the ancient Romans to represent numbers.
Leaving the number being rounded as it currently appears; done when the digit to the right of the number is a 4 or lower digit.
Approximating a large number to a specific place value or whole number.
Increasing the value the number being rounded by 1; done when the digit to the right of the number is a 5 or higher digit.
The use of a.m. and p.m. to determine 24-hour cycle on a 12-hour clock.
This chapter discusses topics that I like to refer to as the idiosyncrasies of health care math. In the health care careers, we encounter:
Objective 2
Review of roman numerals
The use of Arabic numerals is the numbering system most of us have grown up with. It consists of numbers 0 to 9. All other numbers are based on the various combinations and at what place value each digit is placed.
Roman numerals are letters, commonly written with upper-case letters but occasionally written with lower-case letters, to represent a specific number. As the letters are put together, a different number is created (Table 2-1). The use of Roman numerals as a numbering system is as old as the concept of medicine.
Table 2-1
Roman Numerals Compared with Arabic Numerals
| Roman Numeral (Letter) Upper Case and Lower Case | Arabic Numeral |
 |
 |
| I i | 1 |
| V v | 5 |
| X x | 10 |
| L l | 50 |
| C c | 100 |
| D d | 500 |
| M m | 1,000 |
Data from Mulholland JM: The nurse, the math, the meds: Drug calculations using dimensional analysis, St. Louis, 2007, Mosby, and Fulcher RM, Fulcher EM: Math calculations for pharmacy technicians: A worktext, St. Louis, 2007, Saunders.
Do you have problems remembering the Roman numerals for 50, 100, 500, and 1,000? Try this mnemonic: Lovely Cats Don’t Meow.
Do you remember what a period is in math?
Answer: A period is when larger numbers are grouped by three places. The number 564,321 has two periods in it—thousands period and one period.
Why Do We Use Roman Numerals?
Many factors influence when and where Roman numerals are used. Roman numerals are a part of the apothecary system of measurement, which has been used by physicians for writing medication orders. It was common practice to use Roman numerals when writing medications in small dose increments. They were usually written in lower case with a line drawn over the numerals to prevent misinterpretation of the order. The implementation of the Joint Commission’s current guidelines, however, has led to many changes in the way physicians write medication prescriptions to reduce the potential for error. One change has been the elimination of the apothecary system for writing medication orders. Roman numerals continue to be used to identify different clotting factors found in a person’s blood.
| Example: |
 |
| Example: |
 or  |
Be very careful when interpreting medication orders written with Roman numerals or written with both Roman numerals and Arabic numerals. Many errors occur when a V, which represents a 5, is confused with a U, which represents units. (For example, 
[seven] might be confused with 2 units.) This is why many facilities have discontinued the use of Roman numerals when writing medication orders.
How to Write Roman Numerals
Roman numerals have their own set of rules to ensure proper translation of these numeric symbols:
If the letter is repeated, the number of times the letter is written represents the Arabic numeral.
Example:
II = 2
Letters are never to be repeated more than three times.
Express the following Arabic numerals as Roman numerals
1. 7 _______________________________________
2. 5 _______________________________________
3. 8 _______________________________________
4. 11 _______________________________________
5. 15 _______________________________________
6. 42 _______________________________________
7. 65 _______________________________________
8. 100 ______________________________________
9. 2006 _____________________________________
Express the following Roman numerals as Arabic numerals
11. IV _______________________________________
12. CC _______________________________________
13. XXX _____________________________________
14. XIX _______________________________________
15. MVIII _____________________________________
16. LXV _______________________________________
17. VIII _______________________________________
18. XXXII _____________________________________
19. XVI _______________________________________
Objective 3
Military time
Documentation in military time involves converting a traditional 12-hour clock into 24 hours. This eliminates the need to write a.m. or p.m. after a time entry, thereby avoiding confusion. Military time is always written with four digits. The first two digits represent the hour, and the last two digits represent the minutes. A 0 is used as a placeholder for recording time with only three digits.
| Examples: | |
| 1:00 a.m. | 0100 |
| 2:15 a.m. | 0215 |
| 3:30 a.m. | 0330 |
At 10:00 a.m., a 0 is no longer needed as a placeholder. Simply write 1000 for 10:00 a.m. This method is used until 1:00 p.m.
| Examples: | |
| 10:15 a.m. | 1015 |
| 11:45 a.m. | 1145 |
| 12:20 p.m. | 1220 |
As stated before, military time is expressed by converting a 12-hour clock to a clock that counts 24 hours. The conversion begins when the time hits 1:00 p.m., which is referred to as 1300 hours. As you can see from Figure 2-1, each hour is counted from 1300 to 2359. Midnight (12 a.m.) can be documented in two different formats: 2400 or 0000. Your facility’s policy will state which format you should use to document midnight.
| Examples: | |
| 2:15 p.m. | 1415 |
| 3:30 p.m. | 1530 |
| 7:30 p.m. | 1930 |
| 11:58 p.m. | 2358 |
Use of Military Time in Health Care
Why do health care facilities use military time in their documentation? Most health care facilities operate 24 hours a day, 7 days a week, and 365 days a year (Box 2-1). The use of military time reduces documentation errors, medication errors, and treatment errors. Facilities have used a 24-hour clock to differentiate when an order has been written for a.m. or p.m. administration. Many facilities are not open 24 hours a day but are open 12 to 15 hours a day (Box 2-2). Military time is used to identify when a patient has been seen, has been treated, or has had medication dispensed or when follow-up phone calls are made.
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