Table 1: The number of individual measurements from the given reference. The used filter systems are according to Table 2.

Ref.		System
Maitzen (1976)	168	1
Maitzen (1980a)	10	2
Maitzen (1980b)	8	2
Maitzen & Seggewiss (1980)	21	2
Maitzen (1981)	20	2
Maitzen & Vogt (1983)	342	3
Maitzen & Pavlovski (1989a)	16	4
Maitzen & Pavlovski (1989b)	31	4
Pavlovski & Maitzen (1989)	40	4
Schnell & Maitzen (1994)	3	5
Schnell & Maitzen (1995)	14	5
Maitzen et al. (1997)	6	6
Maitzen et al. (1998)	131	7
Vogt et al. (1998)	803	3