I have one field with [ kilometers ].

Sometimes I make a selection of records. With a scriptbutton, I want to calculate the summery of field "kilometer" from the selected records, the result should be shown in a seperate field.

I know this must be done with a calculation -)), but with which one, this is the question for me as beginner...

Since you're doing this as a script, try something like this:

Go to record[First]

Loop

Set variable[$total; $total + kilometer]

Go to record[Next;exit after last]

End Loop

Set field[myTotal;$total]

Note that the field is only set on the last record. I'm not sure exactly what you're proposing here though, so let us know if you need more help.

Why not simply use a summary field = Total of kilometers?

Why not simply use a summary field = Total of kilometers?

yes it looks simple. but how to use a summery field only for selected records?

Not sure what you mean by "selected records". Summary fields summarize the found set of records.