There are several different types of Tape Measure available each designed for different uses;
An absolutely essential hand tool for all trades not just Carpenters. I use mine all day long to obtain accurate measurements when pricing up work initially and then when working on site. I've got a couple of different designs I use depending on what I'm doing/measuring.
I like Stanley Tape measures because I work in both Imperial and Metric and they display both. Also the Stanley Fatmax Tape Measure I use for First Fix/Framing Carpentry has a long 'standout', which means you can extend the tape out quite far and it will stay rigid - good for measuring long lengths or distances on your own. That and I have a smaller more compact PowerLock measuring tape to use for Finish Carpentry too. It's less bulky than a Fat Max when in your pouch, while both have good clear and easy to read measurements and special coatings that make them last longer, important when you're using them every day.
The metal hook on the end of the tape moves backward and forward the same distance as it is thick. This is so when you are measuring in between two walls for example, then hook onto the end of a piece of timber that thickness of the hook is allowed for. So don't take it back to the shop like I once did when you notice this... Its intentional!
I was always taught 'measure twice cut once'. It gets drummed into you so much when you're learning you think 'yeah yeah whatever', and then you cut something expensive..short. I always double check when I'm taking crucial measurements, and it saves me money!
For accuracy when measuring between two points, ensure the tape is tight and doesn't sag in the middle. Get someone to hold one end if this is difficult or bang a nail in to give you something to hook the end of the tape over.
Also, make sure you hold the tape level or plumb. For example, if you were getting a measurement between two walls for a Dado Rail that will be fitted a Metre up off the floor, mark a line up a Metre off the floor at each end and hold the tape at that height. If one ends high and the other low, you'll get a longer measurement than you want.
If in doubt, cut the work-piece a little long. You can always cut more off if need be, its difficult to put it back on! The more experienced you get the better you'll get at judging when to add/take off a bit from your measurements.
There are two different numerical measurement systems - Metric and Imperial. At school I was taught to use Metric but when I was on my apprenticeship I was taught by an old craftsman who still used Imperial measurements. I now tend to work in Imperial, but use Metric when it is easier. Working in Imperial can be pretty complicated when you are calculating Spindle spacings for example where you need to divide measurements.
Metric - Metric measurements are in Millimeters, Centimeters and Meters. There are 10 Millimeters in a Centimeter and 100cm (1000mm) in Meter. When working in Metric you'll generally use Millimeters as that's most accurate. Unless measuring large dimensions.
Imperial - measurements are in Feet and Inches, and fractions of Inches. There are 12 Inches in 1 Foot. Imperial measurements are written in Feet and Inches and abbreviated, so 6'4 1/4" means six Feet four and a quarter Inches.
There are 25mm in 1". If your tape only splits Inches into sixteen segments (like in the picture below) then Metric is slightly more accurate because one inch can be broken down into 25mm. However, some tapes break each inch down into 32 segments, which is then more accurate than Metric. Choosing the system you work with will probably depend on what your colleagues use and what you find easiest to understand.
Above is what you'll find at the beginning of an Imperial Tape Measure. Each Inch is broken down into sixteen segments. In order to read and understand an Imperial Tape Measure, you will need to have a basic understanding of Fractions.
Although every segment is 1/16th of an Inch, you don't read the halfway point as 8/16ths, because you can 'simplify' that Fraction. If both numbers can be divided by one number then that's what you do in order to simplify. Both 8 and 16 can be divided by 8, so 8/16 is also 1/2 Inch.
Here is each increment of one Inch, simplified;
2/16 = 1/8
4/16 = 2/8 = 1/4
6/16 = 3/8
8/16 = 4/8 = 2/4 = 1/2
10/16 = 5/8
12/16 = 6/8 = 3/4
14/16 = 7/8
16/16 = 1 inch
It's confusing at first but becomes second nature after a short while. It does get a little more complicated if you have to add two measurements together. This is fairly straight forward if the bottom numbers of the Fraction are the same,
1/4 + 1/4 = 2/4 or 1/2
2/4 + 3/4 = 5/4 or 1 and a 1/4
If the bottom numbers are different then it takes a little more work;
1/16 + 1/8
Here, you need to make the numbers under the lines the same. Change 1/8 back to 2/16 so they can be added together;
1/16 + 2/16 = 3/16
3/8 + 15/16
Change 3/8 to 6/16 to make it work
6/16 + 15/16 = 21/16 Or 1 and 5/16
Tape measures are marked so you can quickly and easily see where the centers are without having to do too much math in your head! Metric centers are 400, 800, 1200mm and so on. Imperial centers are 16, 32, 48 inches and so on. If you look at the pictures above 400mm is red and also has a small black diamond making it stand out from the rest of the measurements. 16 inches isn't red on this particular tape but it does have a small black diamond, again making it stand out. All you need to do when setting out centers is look for these symbols, making it less likely you'll mark any timbers in the wrong positions.
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