Using est+ with effort estimate range

[Axel Kielhorn]

Hello,

according to the manual, there is a special column type for column view

‘est+’  Add low-high estimates.

This is explained later:

The ‘est+’ summary type requires further explanation. It is used for combining 
estimates, expressed as low-high ranges. For example, instead of estimating a 
particular task will take 5 days, you might estimate it as 5–6 days if you’re 
fairly confident you know how much work is required, or 1–10 days if you do not 
really know what needs to be done. Both ranges average at 5.5 days, but the 
first represents a more predictable delivery.

But I’m not able to define a range.

** Arbeitszeiten planen und erfassen
:PROPERTIES:
    :COLUMNS:  %50ITEM(Aufgabe) %11TODO(Status) %EFFORT{est+} %CLOCKSUM
    :ID: Arbeitszeiten
:END:

*** Aufgabe 2 [0/1]

**** TODO Unteraufgabe 1
:PROPERTIES:
:EFFORT:   3-5 h
:END:

What is the correct format to define a range?

Thanks for your help.

Greetings
Axel