Final answer:
The correct instruction for dosage calculations is to convert grams to milligrams by moving the decimal three places to the right, with liters being a unit of volume, the metric system using decimals, and grains not being a metric measurement.
Step-by-step explanation:
The correct instruction to include when converting measurement units in dosage calculations is: To convert g to mg, move the decimal 3 places to the right. Liters are a unit of measurement for volume, not distance. The metric system commonly uses decimals rather than fractions for easier conversion between units. Grains are not used in the metric system but are part of the imperial system and are a unit of weight measurement.
Unit conversion is essential in medicine for accurate drug dosing. For example, when instructed to administer a dosage of 0.2 grams (g) of aspirin, and given 50 mg tablets, the nurse needs to know that 0.2 g equals 200 mg, requiring the administration of 4 tablets. Converting from liters to milliliters involves moving the decimal three places to the right, and vice versa for milliliters to liters. Such conversions are critical to avoid dosing errors, potentially critical in medical settings.