A person who has a substantial connection has enjoyed the benefits of citizenship, such as receiving an education here from young, or retains links to the country, such as one's family residing here.

Justice Chan declined to give benchmarks for Singaporeans who left the country at a young age and had little connection to the country.

According to the Enlistment Act, anyone who fails to fulfil his NS obligation could face up to three years in prison or a fine of up to $10,000, or both. But Justice Chan, in his judgment, produced a graph charting benchmark prison terms against the number of years a defaulter has stayed away without a valid exit permit. Key factors to take into account are if the offender voluntarily surrendered or was arrested, and if he pleaded guilty or claimed trial.

The age of the offender should also be taken into account. The older he is, the higher the baseline sentence should be, since he would likely have lower fitness over the course of his NS, including reservist.

The judge also highlighted a "discount" range for offenders who produced an "exceptional" performance in NS. Depending on the age of the defaulter, these discounts range from two months for those below 20, to half a month for offenders between 35 and 40 years of age.

So, someone prosecuted after the age of 38, for instance, after he was arrested and claimed trial, could face a jail term closer to the maximum three years.

In Chow's case, Justice Chan said that he would have been jailed for three months, if not for his exceptional performance during his NS.

EQUITY AND UNIVERSALITY

Describing NS as the cornerstone of Singapore's defence and security, Justice Chan highlighted the three principles underpinning NS - national security, equity and universality.

He explained that NS has to be served in accordance with the prevailing defence policy, which is set by the Defence Ministry (Mindef), and it was not open to an individual to choose unilaterally when he would discharge his obligations.

Universality boils down to the idea that all who are fit to serve NS must serve. Otherwise, it could lead to feelings of unfairness and undermine morale and commitment among those who have to serve NS.

Equity requires that everyone be treated in the same way under the NS regime.

"NS is about each Singaporean male citizen performing his fair share towards Singapore's national defence, regardless of his background or circumstances," said Justice Chan, adding that this also involves sacrifice on the part of enlistees to postpone their personal goals, including continuing their education, to fulfil their duties.

As for ruling that prison is warranted for those who defaulted on NS for more than two years, the judge pointed to Mindef's statement delivered by then Defence Minister Teo Chee Hean in Parliament in 2006, to address the public outcry over pianist Melvyn Tan receiving just a $3,000 fine for evading NS.

Having gone to England in 1969 at the age of 12 to study music, Mr Tan did not return for 28 years. He was arrested after returning here in 2005 at the age of 49, as a British citizen, to visit his ageing parents.

SPLIT VIEWS

Parents with children studying overseas saw the jail term for Chow as harsh, but those whose children are being educated locally called it lenient. Ms Geraldine Shum, 50, who has a 19-year-old in NS, believes the jail term should have been longer. "It was unfair for him to complete his university studies first, when his peers have to serve."

But engineer Chua Kim Loong, who lives with his family in Australia and has two teenage sons, believes jail for Chow was too strict.

"It is ridiculous that someone who came back to serve, and with distinction, can still be jailed. He may lose his sense of belonging to this place after being in prison," said the 45-year-old.

Housewife Julie Koh, 52, who has a 13-year-old son who intends to return from the United States to serve his NS, added that she knew of young Singaporean men who defaulted and have no intention of coming back. "They basically get away scot-free. But the boy in this case came back."

DETERRENCE

Some NSmen also agreed that jail was not appropriate, since the black mark would remain with the 25-year-old after serving his time.

Said 26-year-old student Daryl Zeng, who returned to Singapore in 2008 to serve his NS after seven years in Australia: "A jail term could ruin one's future prospects."

But 21-year-old student Mark Ng, who returned for NS in 2010 after living abroad for over five years, said a fine was not enough of a deterrent, "especially considering that those who can afford to study overseas usually come from affluent families".

• NS REQUIREMENTS

• Every Singaporean male must do national service.

  Between 13 and 161/2 years old

  • An exit permit is needed for overseas travel of three months or longer

  • A bond of $75,000 or half of the parents' combined annual gross income for the preceding year, whichever is higher, is required if the child is out of the country for two years or longer.

  Older than 161/2 but yet to enlist

  • Exit permit and bond are required for overseas travel of three months or longer.

  At 16 1/2 years old

  • A letter will be sent to inform individual about registering via the NS portal. Registration is scheduled by birth date.

  • Complete pre-enlistment documentation and book a date for medical screening. • Prepare and take physical proficiency test before enlistment.

  • Apply for deferment if taking the GCE A levels, full-time diploma or equivalent.

  Two months before enlistment

  • Enlistment notice, with details like reporting time and venue, is sent two months before scheduled enlistment date. Individuals must report to camp on the date of enlistment.