Heiskanen, W. <br/><br/>
Topographic-isostatic reduction maps for europe and north atlantic in the hayford zones 18-1 for the airy-heiskanen system, t= 30 km and 20 km 

 - Helsinki :   Suomalainen Tiedeakatemia,   1959. 
 - 4 p. :   maps. ;   22 cm. 
 - Annales Academiae Scientiarum Fennicae ;   54 .