measurement in Spain

your nurse's meter reading is in milligrammes per decilitre mg/dl
Your meter is in millimoles per millilitre.
Without getting too technical, think of it as like using yards and metres.
The preferred unit varies from country to country. Many countries other than the US use mg/dl/ (list on wiki if you're interested http://en.wikipedia.org/wiki/Glucose_meter)

No new meters sold in the EU allow you to toggle between the two readings (you used to about 8 years ago but there were reported instances of people becoming confused so the EU regulated against it)

To change mg/dl to mmol/l you divide by 18
To change mmol/l to mg/dl you multiply by 18
or you use a converter like this one
http://www.diabetes.co.uk/blood-sugar-converter.html
123mg/dl / 18 =6.8mmol/l


If you get lab blood tests in Spain check the unit carefully. Cholesterol might be in mg/dl (or even more confusing g/l as it is here in France but I think they are the only country I know that do that)
The conversion factor is not the same .
Heres one for cholesterol
http://www.onlineconversion.com/cholesterol.htm