reading the numbers and graduations carefully on a tape measure, to make sure that you are taking off the correct measurement from the correct section of the tape. Below are some more suggestions for making sure that the measurements you take are accurate and correct. Reading dials and gauges A common error when reading dials or gauges is to look at the pointer from an angle to the scale. This means that instead of reading off the mark immediately behind the pointer, you read a mark that is either on the left or right hand side of the pointer. The problem is called parallax error, because refers to the way an object ‘parallax’ seems to change its position when your own point of observation changes. Some instruments have a mirror on the dial so that you can line up the pointer with its own reflection, to make sure that your reading is exactly at right angles to the scale. Even if there a mirror, the simple solution to the problem is to use one eye only isn’t and make sure looking at the scale at exactly 90 degrees. you’re It is even possible to get a parallax error with a ruler or tape measure if the graduations are not hard against the mark or edge that you want to measure. Again, always make sure that your eye is at 90 degrees to the scale when you take the measurement. In the case of the tape measure, you should also push down the steel blade so that the top edge is flat against the object measuring. you’re Calibrating instruments Some measuring instruments need to be calibrated before they are used. This often means adjusting the zero mark on the gauge to correspond with a true zero reading. Weighing scales are an example of an instrument that must be set to zero before you start taking measurements. Some instruments also need to be adjusted differently for particular types of materials. For example, moisture meters for timber use different scales depending on the species of hardwood or softwood being measured. The simplest way of making these sorts of allowances is to have a conversion chart that enables the user to add or subtract amounts to give a reading. ‘corrected’ cut ‘Measure twice, once’
reading the numbers and graduations carefully on a tape measure, to make sure that you are taking off the correct measurement from the correct section of the tape. Below are some more suggestions for making sure that the measurements you take are accurate and correct. Reading dials and gauges A common error when reading dials or gauges is to look at the pointer from an angle to the scale. This means that instead of reading off the mark immediately behind the pointer, you read a mark that is either on the left or right hand side of the pointer. The problem is called parallax error, because ‘parallax’ refers to the way an object seems to change its position when your own point of observation changes. Some instruments have a mirror on the dial so that you can line up the pointer with its own reflection, to make sure that your reading is exactly at right angles to the scale. Even if there isn’t a mirror, the simple solution to the problem is to use one eye only and make sure you’re looking at the scale at exactly 90 degrees. It is even possible to get a parallax error with a ruler or tape measure if the graduations are not hard against the mark or edge that you want to measure. Again, always make sure that your eye is at 90 degrees to the scale when you take the measurement. In the case of the tape measure, you should also push down the steel blade so that the top edge is flat against the object you’re measuring. Calibrating instruments Some measuring instruments need to be calibrated before they are used. This often means adjusting the zero mark on the gauge to correspond with a true zero reading. Weighing scales are an example of an instrument that must be set to zero before you start taking measurements. Some instruments also need to be adjusted differently for particular types of materials. For example, moisture meters for timber use different scales depending on the species of hardwood or softwood being measured. The simplest way of making these sorts of allowances is to have a conversion chart that enables the user to add or subtract amounts to give a ‘corrected’ reading. ‘Measure twice, cut once’