A royal proclamation of King Rama VI of Siam dated 17 May 1930 <a href="https://en.wikipedia.org/wiki/Common_Era" class="extiw" title="w:Common Era">CE</a>, amending details regarding provisional apprehension of criminals under the expedition treaty between Siam and Britain dated 4 March 1911 <a href="https://en.wikipedia.org/wiki/Common_Era" class="extiw" title="w:Common Era">CE</a>, as published in the Siamese  Government Gazette on 18 May 1930 <a href="https://en.wikipedia.org/wiki/Common_Era" class="extiw" title="w:Common Era">CE</a>.
Government of Siam
1930-05-18
<a rel="nofollow" class="external text" href="http://www.ratchakitcha.soc.go.th/DATA/PDF/2473/A/14.PDF">Royal Siamese Government Gazette, volume 47, part 0 A, dated 18 May 1930, pp. 14–21.</a>