# LAYING OUT A CALIBRATION COURSE

(This is 1 webpage from over 50 web pages at coursemeasurement.org.uk which are used to train measurers. It describes the careful procedure that is needed to establish an accurate calibration course with an error of less than 0.02%)

Lessson 1.2 Layout and Taping of a Calibration Course

To layout a Calibration Course you need the following core items of equipment

• Steel surveyor's tape 30m or 50m long. Do not use a tape with a plastic scale, this will not be accurate enough since they stretch under tension and as the temperature rises much more than a steel tape does.
• Nails to mark the ends of the course, and to use to mark each tape length + club hammer to knock the nail into the road
• Notebook and pencil to record readings of the tape.
• A spring balance with which to tension the tape at 50N ( an N is a Newton which is the same as about 11 lbs or 5kg on your spring scale)
1. Hammer a nail in at one end, leaving enough room to hook the tape ring over the nail. This is NAIL 1.
2. You need to know the end correction for your tape. It will remain fixed so you only ever have to measure it once. Here is how:-

With the tape hooked over the nail, measure from say the 100mm mark to the centre of the nail. (I have used a yellow spring tape in the picture above) In this case the distance from the 100mm mark to the centre of the nail is 95 mm. Therefore I have to SUBTRACT 5 mm from each tape length to correct for the end reading.
3. Leaving the ring end hooked on the nail, go to the other end of the tape and pull it straight and untwist it if necessary. Place the tape on the ground and hammer in NAIL 2 close to (or just less than) the end mark on the tape. In the picture below it is being inserted more less at the 50m mark:-
4. Now use the spring scale to tension the tape at 50N (approx 5kg). The tension does not have to be very accurate. The tape will stretch by 5 to 10 mm depending on its cross-section. With practice you will find that you can hold the spring balance with one hand, and hopefully get your head over the nail so you will be able to see the tape reading..
5. Now, keeping the tension read the scale at the centre of the nail. This reads 49.992 m