How to find length of a field of an object?

I have an object that contains signal values. I want to find the length of the signal inbetween two elements in the field called uppFWHMSignal and lowFWHMSignal.

function FWHM(Obj,signal)
StartCellNumber=1;
EndCellNumber=length(Obj.Data);
for CellNr=StartCellNr:EndCellNr                
    for iFrame=1:length(Obj.CompCellList{CellNr})%ib:id
        Obj.Data{CellNr}{iFrame}.([signal,'uppFWHMSignal'])= max(max(Obj.Datat{CellNr}{iFrame}.(signal))/2);
        Obj.Data{CellNr}{iFrame}.([signal,'lowFWHMSignal'])= min(max(Obj.Data{CellNr}{iFrame}.(signal))/2);
        Obj.Data{CellNr}{iFrame}.([signal,'length'])=length(Obj.Data{CellNr}{iFrame}.(signal)); %length of the signal
    end   
end
end

Thank you