Missing description of identifier 'pi'

[Regina Henschel <rb.henschel@t-online.de>]

Hi all,

section 19.171 draw:formula in part 1 lists in Table 1 the identifiers 
with a description. The identifier 'pi' is missing there. Of cause 
everyone will expect the value π there. But it might be necessary/useful 
to determine an minimum accuracy for this constant.

Kind regards
Regina