"第幾"

https://groups.google.com/d/topic/alt.usage.english/Ve_mmYlyHDM/discussion
[quote]
"Where do you come in your family?" (a bit vague but probably understandable)
"Where do you ....
"Where do you ...
[end quote]


https://groups.google.com/d/topic/alt.usage.english/qdOnNxBlcaA/discussion

https://groups.google.com/d/topic/alt.usage.english/LnZVdAPGhN4/discussion
[quote]
This question is asked here about once a month.  There is no English
question word for the concept.
[end quote]

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"Practical English Usage" by Michael Swan, 3e, page 228
252.5 ......
[quote]
Note that English does not have a special expression to ask for ordinal numbers (first, second etc).

It's our wedding anniversary. ~Congratulations. Which one? (NOT ... the how manyeth?) 

[end quote]

diopter value

逛Mall時在Sears的男裝部門一個角落看到這個算是很尋常的reading glasses展示/販售架。顧客可以自己戴著試，滿意了直接拿去附近櫃台結帳
(我的便宜手機的相機解析度看樣子不甚好...)

以下出現的 strength 字眼相當於我們平常講的(眼鏡)度數:

To Choose Your Correct Strength:

* If you are wearing glasses, remove them.
* Read down the chart to the right at your normal reading distance, about 14 inches
* When the text becomes difficult to read, note the diopter figure on the left.
* The diopter value indicates the strength of the lens that your require.
* Select this strength from the display and check for comfort.
--------
WEAK    +1.25    If you cannot read this line .....
MEDIUM    +1.75    If you cannot read this line .....
MEDIUM    +2.25    If you cannot read this line .....
STRONG    +2.75    If you cannot read this line .....
--------
下方展示架上有很多reading glasses(老花眼鏡)(上頭有貼度數標籤)

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另一個賣場看到的:

Step 1 Remove your glasses and step back approximately 14 inches away from the eye test chart.

Step 2 Read the lines starting at the top. The first line that you have trouble reading has the lens' strength to the left. That is your correct strength.

Step 3 Find your glasses easily with our color-coded strength labels.