def conventions(modul):
    """
    Create dictionary with unit conventions for expected physical quantities.

    Parameters
    ----------
    modul : {'E', 'G'}
        Indicates wether tensile ('E') or shear ('G') modulus data are provided.

    Returns
    -------
    conv : dict of {str : str}
        Contains the names of the physical quantities as key and 
        the corresponding names of the units as item.

    Notes
    -----
    Tensile moduli are denoted as 'E' and shear moduli  are denoted as 'G'. 
    Only the tensile moduli are summarized in the table below. For shear modulus 
    data, replace 'E' with 'G', e.g. 'E_relax' -> 'G_relax'.

    ========================  ========  =================== 
    Physical quantity         Variable  Unit                  
    ========================  ========  =================== 
    Relaxation modulus:       E_relax   [Pa, kPa, MPa, GPa] 
    Storage modulus:          E_stor    [Pa, kPa, MPa, GPa] 
    Loss modulus:             E_loss    [Pa, kPa, MPa, GPa] 
    Complex modulus:          E_comp    [Pa, kPa, MPa, GPa] 
    Loss factor:              tan_del   -                   
    Instantaneous modulus:    E_0       [Pa, kPa, MPa, GPa] 
    Equilibrium modulus:      E_inf     [Pa, kPa, MPa, GPa] 
    Angular frequency:        omega     rad/s               
    Frequency:                f         Hz                  
    Time:                     t         s                   
    Temperature:              T         °C                  
    Relaxation times:         tau_i     s                   
    Relaxation moduli:        E_i       [Pa, kPa, MPa, GPa] 
    Norm. relaxation moduli:  alpha_i   -                   
    Shift factor:             log_aT    -        
    ========================  ========  ===================            
    """
    m = modul
    conv = {'f' : ['Hz'],
            't' : ['s'],
            'omega' : ['rad/s'],
            'T' : ['°C', 'C'],
            'tau_i' : ['s'],
            'alpha_i': ['-', ''],
            'tan_del': ['-', ''],
            'log_aT': ['-', ''],
            '{}_relax'.format(m): ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_stor'.format(m):  ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_loss'.format(m):  ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_comp'.format(m):  ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_0'.format(m):     ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_inf'.format(m):   ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_i'.format(m):   ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_relax_filt'.format(m): ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_stor_filt'.format(m):  ['Pa', 'kPa', 'MPa', 'GPa'],
            '{}_loss_filt'.format(m):  ['Pa', 'kPa', 'MPa', 'GPa'],
            'Set' : ['-', ''],
            'RefT' : ['°C', 'C'],
            'C1' : ['-'],
            'C2' : ['°C', 'C']}
    return conv