The Estimated Number

Everyone knows how to measure, but in science we measure as far out as we can. This means that when you run out of tickmarks on a device such as a ruler, we estimate the final number.

Why? This tells us how precise the instrument you used to measure actually is. You probably wouldn't want to measure the length of a classroom in miles or killometers.. so an instrument that only measured to the mile or kilometer would be useless in that case (you could only estimate the feet or meters).

Read the following to help show you how to find the estimated number:

Estimated Number in 4 Steps..

Step 1:

make sure you are on the metric side!

Step 2:

Count how many whole numbers from the biggest tick marks the line goes past, put that number down and a decimal point

1.

Step 3:

Count how many of the next smallest tick marks the line goes past (red tick marks). Put that number in the tenths place.

1.9

Step 4: Oh no! We're out of tick marks on this ruler! That means we need to write the ESTiMATED NUMBER. You do this by imagining in your head that there are tick marks (from 0-9) between 1.9 cm and 2.0 cm (the blue area below).

To me, this looks like it is maybe a 2 so I write it like this:

1.92

You might think it looks like 1.93 or 1.91 ...guess what? Those are all acceptable answers!

The estimated number is always the number that cannot be identified by a tick mark (or graduation) on the ruler.

"1.92 "

We're done right??

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but wait!

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Eek, this answer is naked!

VERY LAST STEP:

If I were your esteemed colleague, I would have no idea what kind of measurement this is! Don't forget your units for full credit!

1.92 cm

Done ;)

A few notes... you must measure out to the estimated number. This is to say that you physically LOOKED at each tick mark and measured accurately. This is sometimes referred to as the level of precision. If the number you measured was EXACTLY on the 2 centimeter line on the ruler above, I would have had to write 2.00 cm. This means that I could actually see millimeters - I didn't estimate them! This comes in handy when you need to measure something very small... if the bolded zero wasn't there I would assume that you estimated how far between centimeters instead. You not only wouldn't get very precise measurement, but all of your effort of actually measuring would be wasted!

Still confused? Check out this video:

(remember to stop where your confused, take notes and rewatch from that point!)