水草情迷

I have a question about the arctica cooler. the shop told me how to use it, but it is totally different from the menu.
There is two things you have to set, right?
1. current water temp. (same as the theometer)
2. target temp. (On the menu, it said that the cooler with be on/off by +1/-1 degree. If i set 26, it will turn on when water temp is 27 and turn off when it is 25, right)
the above is what i found from the menu. So +1/-1 degree is fixed and can't be adjust, right?
The shop keep saying it is not necessary to set the current temp. as the cooler got the theometer. if the machine shows 26, you set it 28 (two degree difference, this is what he keep telling me), then it will be +1/-1 degree on/off. it doesn't make sense to me, as why don't you set 24 to get it +1/-1 degree on/off.

Can anyone tell me is it right from the menu?
Now, I set 26 degree for my tank. So, is it on when 27 and off when 25?

sorry,睇完唔係好明後尾果段寫乜。
我係用200的，同150應該一樣掛，
原廠設定係+0.5度著機，無得改，
即係set26度，26.5度著機，降到25.9度停機。

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咸水：
48" FOT: (450L) 2006年6月 - 2009年8月完
24" RT (150L) 2009年10月 - 2010年2月完
淡水：
16" 水草+蝦缸 (26L) 2009年9月
24" 水草+鯛缸 (90L) 2010年4月
update on 2010-06-17