How To Calculate Percentage Error Of A Balance
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Volumetric Glassware and Devices to Deliver Volumetric Glassware and Devices to Contain Nonvolumetric Glassware and Devices Guidelines for Selection References Weighing It is 50cm3 measuring cylinder uncertainty generally agreed that pharmaceutical products should be prepared with a 100 cm3 measuring cylinder uncertainty low percentage of error. The official compendia allow a tolerance of ± 5% for most formulas, pipette uncertainty although greater accuracy may be required for very potent drugs with greater toxicity potential. This same degree of accuracy is expected in all extemporaneously compounded http://www.thestudentroom.co.uk/showthread.php?t=203747 products. Most pharmaceutical products allow for a tolerance of only 5% error, where If we know the sensitivity of the balance (i.e. the potential error) we can calculate the percentage of possible error when any amount of the substance is weighed. e.g. The Class III prescription balance has a sensitivity of 6 http://pharmlabs.unc.edu/labs/measurements/weigh.htm mg. What % of error would result in weighing 50 mg of a drug on the balance? Similarly, we can calculate the smallest quantity that can be weighed, on a balance of known sensitivity, to maintain a desired level of accuracy. This weight is referred to as the least weighable quantity (L.W.Q.). e.g. What is the least weighable quantity that will result in an error of 5% or less on a Class III prescription balance? You should keep this figure in mind for the remainder of your career. When a prescription formula calls for the incorporation of a component weighing less than 120 mg, special methods must be employed to obtain that weight of the component. If a liquid dosage form (solution, suspension or emulsion) is being prepared, the liquid aliquot method is employed. When the component must be incorporated as a solid into powders, tablets, capsules, or pastes, the trituration method is used.
The difference between two measurements is called a variation in the measurements. Another word for this variation - or uncertainty in measurement - is "error." This "error" http://www.regentsprep.org/regents/math/algebra/am3/LError.htm is not the same as a "mistake." It does not mean that you got the wrong answer. The error in measurement is a mathematical way to show the uncertainty in the measurement. It http://www.webassign.net/question_assets/unccolphysmechl1/measurements/manual.html is the difference between the result of the measurement and the true value of what you were measuring. The precision of a measuring instrument is determined by the smallest unit to which it percentage error can measure. The precision is said to be the same as the smallest fractional or decimal division on the scale of the measuring instrument. Ways of Expressing Error in Measurement: 1. Greatest Possible Error: Because no measurement is exact, measurements are always made to the "nearest something", whether it is stated or not. The greatest possible error when measuring is considered to be one half of percentage error of that measuring unit. For example, you measure a length to be 3.4 cm. Since the measurement was made to the nearest tenth, the greatest possible error will be half of one tenth, or 0.05. 2. Tolerance intervals: Error in measurement may be represented by a tolerance interval (margin of error). Machines used in manufacturing often set tolerance intervals, or ranges in which product measurements will be tolerated or accepted before they are considered flawed. To determine the tolerance interval in a measurement, add and subtract one-half of the precision of the measuring instrument to the measurement. For example, if a measurement made with a metric ruler is 5.6 cm and the ruler has a precision of 0.1 cm, then the tolerance interval in this measurement is 5.6 0.05 cm, or from 5.55 cm to 5.65 cm. Any measurements within this range are "tolerated" or perceived as correct. Accuracy is a measure of how close the result of the measurement comes to the "true", "actual", or "accepted" value. (How close is your answer to the accepted value?) Tolerance is the greatest range of variation that can be allowed. (How much error in the answer is occurr
brothers, and 2 + 2 = 4. However, all measurements have some degree of uncertainty that may come from a variety of sources. The process of evaluating the uncertainty associated with a measurement result is often called uncertainty analysis or error analysis. The complete statement of a measured value should include an estimate of the level of confidence associated with the value. Properly reporting an experimental result along with its uncertainty allows other people to make judgments about the quality of the experiment, and it facilitates meaningful comparisons with other similar values or a theoretical prediction. Without an uncertainty estimate, it is impossible to answer the basic scientific question: "Does my result agree with a theoretical prediction or results from other experiments?" This question is fundamental for deciding if a scientific hypothesis is confirmed or refuted. When we make a measurement, we generally assume that some exact or true value exists based on how we define what is being measured. While we may never know this true value exactly, we attempt to find this ideal quantity to the best of our ability with the time and resources available. As we make measurements by different methods, or even when making multiple measurements using the same method, we may obtain slightly different results. So how do we report our findings for our best estimate of this elusive true value? The most common way to show the range of values that we believe includes the true value is: ( 1 ) measurement = (best estimate ± uncertainty) units Let's take an example. Suppose you want to find the mass of a gold ring that you would like to sell to a friend. You do not want to jeopardize your friendship, so you want to get an accurate mass of the ring in order to charge a fair market price. You estimate the mass to be between 10 and 20 grams from how heavy it feels in your hand, but this is not a very precise estimate. After some searching, you find an electronic balance that gives a mass reading of 17.43 grams. While this measurement is much more precise than the original estimate, how do you know that it is accurate, and how confident are you that this measurement represents the true value of the ring's mass? Since the digital display of the balance is limited to 2 decimal places, you could report the mass as m = 17.43 ± 0.01 g. Suppose you use the same electronic balance and obtai