Because the mobus Binding doesn’t appear to support transforms so you will have to create a proxy Item and a rule to divide it by 10.
Number TempProxy "Test2 [%.1f]°C" (EG_Flur)
Number ist_Temperature_Raum_1 {modbus="slave1:0"}
rule "Adjust Temp"
when
Item ist_Temperature_Raum_1 received update
then
TempProxy.sendCommand((istTemperature_Raum_1.state as DecimalType) / 10)
end
You could create a lambda (i.e. function) but if all you are doing is dividing by 10 it will probably be less work and less lines of code to just do it inline in the rule.