Measuring---absolute error

Since the unit of the measure is 2cm,
the maximum absolute error of the measurement is 2cm / 2 = 1cm

For example, the length of the cylinder is 8cm,
then the true length of the cylinder lies between 7cm and 9cm.

2009-06-17 11:37:25 補充：
When the unit of the measure is 2cm, it means that the measuring tool is a 2cm scale ruler such that the scale of this ruler is at an interval of 2cm and there is no sub-division ( or mark ) between 2cm. In short, the smallest unit of measurement is 2cm.

2009-06-17 11:37:57 補充：
This ruler is not a precise/accurate instrument. Measurement made with this ruler is accurate to 2cm, in other words, the measure can only be corrected to 2cm.

2009-06-17 11:38:32 補充：
The absolute error is expected to be 1/2 above or below the smallest unit of measurement.
Since the smallest unit of measurement is 2cm, the absolute error is 1cm.

2009-06-17 16:34:04 補充：
I agree with 石石's opinion and that is why I put down "the maximum absolute error of the measurement is 2cm / 2 = 1cm." as the answer.

2009-06-17 16:37:36 補充：
I need to revise my supplement as follows :
The MAXIMUM absolute error is expected to be 1/2 above or below the smallest unit of measurement.
Since the smallest unit of measurement is 2cm, the MAXIMUM absolute error is 1cm.

abs. err = true value - measured value
MAX. abs. err. = scale interval/2.........

how come that you can find a abs. err.?

Since the measurement is 2 cm. ( or cm^2 whatever it is), that means the scale interval is 1 cm. So max. absolute error = 1/2 = 0.5 cm.