Calculating Measurement Error for a Digital Lux Meter

[AltruisticVariation]

Homework Statement

For my lab report I am asked to calculate the error of a couple of measurements which I did with a lux meter. I know that the lux meter has tolerance(or accuracy?) 5%. The instrument is digital and it's last digit is 0.1. The maximum reading is 47.5 lux.

Homework Equations

:

The Attempt at a Solution

:[/B][/B]
Is the error 5% of each measurement? Should I add reading error? I'm pretty confused, sorry if it's a silly question.

 

[haruspex]

Is the error 5% of each measurement?

Do you mean, are the errors on different readings independent? Hard to know without knowing how the device works and what its chief source of error is, but I would expect some degree of systematic error.

Should I add reading error?

How is the reading done? Is it a digital readout or a sweeping hand on a dial?

 

[AltruisticVariation]

Edited the post. The professor said that the error is 5%, nothing more and now I can't figure it out.

 

[haruspex]

Edited the post. The professor said that the error is 5%, nothing more and now I can't figure it out.

Then take is as independent on each reading.
Just noticed you did state it is a digital readout. You mention the last digit is 0.1, but that doesn't help without knowing how large a typical reading is.

 

[AltruisticVariation]

Then take is as independent on each reading.
Just noticed you did state it is a digital readout. You mention the last digit is 0.1, but that doesn't help without knowing how large a typical reading is.

What do you mean by independent on each reading? 5% of each reading? The minimum value is 0 and the maximum 47.5. So the bigger the reading the bigger the error? For example what is the error when the reading is 0?

 

[haruspex]

the bigger the reading the bigger the error?

That's what is usually meant by 5%.

What do you mean by independent on each reading

Measuring devices tend to have some systematic error. E.g. all readings tend to be, say, 1% over; or all tend to be so much under, etc.
Independent would mean that the error in one reading is unrelated to errors in other readings.

 

[AltruisticVariation]

That's what is usually meant by 5%.

Measuring devices tend to have some systematic error. E.g. all readings tend to be, say, 1% over; or all tend to be so much under, etc.
Independent would mean that the error in one reading is unrelated to errors in other readings.

Well yes possibly then we suppose we have no systematic error. Generally the devices were in pretty bad situation so the professor told us to consider the error 5%.
So should I add the reading error (+0.1 to all errors)? That makes sense to me.

 

[haruspex]

Well yes possibly then we suppose we have no systematic error. Generally the devices were in pretty bad situation so the professor told us to consider the error 5%.
So should I add the reading error (+0.1 to all errors)? That makes sense to me.

It depends. If a reading is 100 then the ±5% is going to make the ±0.05 irrelevant.

 

[AltruisticVariation]

It depends. If a reading is 100 then the ±5% is going to make the ±0.05 irrelevant.

Yes sure. So the reading error isn't 0.1 that I thought?