``I would like to refer to the failure of the seismic network to detect small-yield explosions because of hardware limitations and the incorrect estimation by some -- though not all -- foreign seismologists of the yields of separated, simultaneous explosions because of software and analytical inadequacies.''

The AEC Chairman was addressing scientists of the Bhabha Atomic Research Centre (BARC) on the institution on the occasion of Founder's Day -- the birth anniversary of Dr Homi Bhabha, architect of the Indian nuclear programme.

The Chairman's statement comes at a time when some international scientists have said that the total yield of the Indian tests was just one fourth of the 60 KT that were being claimed.

Dr Chidambaram said that as a responsible country, India'snon-proliferation credentials were impeccable. ``We have never exported any equipment or technology to any country which has then misused it.'' This was because Indian export controls were strict and effective, which had led one of his western friends to comment that India was a ``classic non-proliferator''.

Later informally speaking to newspersons, Dr Chidambaram said that the thrust in India should be to develop three standard designs for nuclear weapons which had been successfully tested at Pokharan: a thermonuclear or hydrogen bomb, a fission device and sub-kiloton devices. (The US has over 70 designs for nuclear weapons including those for ballistic and cruise missile warheads, nuclear depth charges, torpedoes, rockets, artillery shells, landmines and even briefcase devices).

He maintained that the total yield of the five tests on May 11 and 13 were around 60 KT and the yield of the thermonuclear device, commonly known as the hydrogen bomb was 45 kt. The thermonuclear device was a two-stage systemusing a boosted fission device as the first stage and the total yield of the device could be raised to 200 kt or even more.

When asked whether the tests had generated sufficient data to simulate explosions on computer he said that there was no difference between design calculation and computer simulation since physics was involved in both. The days where explosions were required to validate design calculations were long gone, he said.

He said that India was forthcoming in giving details of the Pokharan-II nuclear tests, and these were of 1998-vintage. The robust designs were based on current knowledge of physics, materials science, engineering and electronics. Not not only several seismic stations of the meteorological department has endorsed the tests but India also had details from seven accelerometers and five geophones close to the shafts. The details received from the recorded data of accelerometers would be released soon, he said.