# (the / a / -) mean time

#### TommyGun

##### Senior Member
Hi,

I am going to write the following sentence in a report:

1. This test measures the mean time of a machine cycle.

But I am in doubt that the article is used correctly. "mean time" is not a precise characteristic and will randomly vary on different executions. So, it may be correct to use an indefinite article:

2. This test measures a mean time of a machine cycle.

Still, it is not the whole difficulty. "mean time" could be perceived uncountably, then the following sentence seems right:

3. This test measures mean time of a machine cycle.

Which version would you prefer?

• #### Thomas Tompion

##### Senior Member
I wonder if you are saying that the test measures the average time of a machine cycle.
.

#### Myridon

##### Senior Member
The mean time is the same as the average time. You would time a lot of cycles and find the arithmetic mean of those numbers. That doesn't seem to match your description as you seem to be concerned about the individual times being different.

#### PaulQ

##### Banned

A mean [time] and an average [time] are the same thing = [the sum of the numbers within a set] divided by [the number of numbers within the set]

"mean time" is not a precise characteristic and will randomly vary on different executions.
I do not understand this at all. You cannot have a "mean time" of one operation. A mean time is a function of the timings of numerous operations. (NB A mean time (countable) )

3. This test measures mean time of a machine cycle.
3. This test measures the mean time of a machine cycle. To obtain a mean time, many cycles have to be measured and then an average is taken of those times.

#### TommyGun

##### Senior Member
It is interesting about "mean" and "average".
I think that they are synonym here, "mean" is even closer to the point because it reflects how it works: for several cycles the running times are measured, then the measurements are summarized and divided by the number of cycles.

I do not understand this at all. You cannot have a "mean time" of one operation. A mean time is a function of the timings of numerous operations. (NB A mean time (countable) )
I understand you confusion, by "mean time" I mean the mean time of a set of measurements.
We run the machine cycle several times, write down the time of each execution and calculate the mean.

In "mean time of a machine cycle," "a machine cycle" is a generalization here. It can be rewritten as "This test measures the mean time of a set of machine cycles," but then there would be no questioning of the article, "the" would be the only choice.

Now I start to doubt whether this is a legitimate generalization, is it?

My concern about the "the" article in variant 1 is following:
We don't use "the" with indefinite objects, obviously.
"mean time of a machine cycle" should be read as "mean time of a set of measurements".

Each running of the test spawns its own measurements, so that the mean of the measurements can be different for different test executions. The mean varies with test executions, and therefore it should be indefinite in the general sense of a single execution. That's why I think variant 2 with "a mean" could be right.

#### Thomas Tompion

##### Senior Member
One slight problem here is that we talk of Greenwich mean time and we talk of things happening in the meantime, so, for me, if you wish to talk about the average time, you are better talking about the average time, and leaving mean times to more intrepid folk.

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