 In 1771 , using the combined 1761 and 1769 transit data , the French astronomer Jérôme Lalande calculated the astronomical unit to have a value of 153 million kilometers ( ± 1 million km ) . The precision was less than had been hoped for because of the black drop effect , but still a considerable improvement on Horrocks ' calculations . 
 In 1771 , using the combined 1761 and 1769 transit data , the French astronomer Jérôme Lalande calculated the astronomical unit to have a value of 153 million kilometers ( ± 1 million km ) . The precision was less than <a href='been_done' title='1'><mark>had</mark></a> been hoped for because of the black drop effect , but still a considerable improvement on Horrocks <a href='null_genetive' title='2'><mark>'</mark></a>calculations . 
In 1771 , using the combined 1761 and 1769 transit data , da French astronomer Jérôme Lalande calculated the astronomical unit to have a value of 153 million kilometers ( ± 1 million km ) . Tdaprecision was less than done been hoped fa bc of the black drop effect , but still a considerable improvement on Horrocks  calculations .