Though we think of a font as a set of char­ac­ters with a uni­form vi­sual ap­pear­ance, the gen­e­sis of these char­ac­ters is any­thing but uni­form. Our writ­ing sys­tem brings to­gether char­ac­ters that were orig­i­nally hand­writ­ten by peo­ple in dif­fer­ent coun­tries, in dif­fer­ent cen­turies. To achieve a uni­form ap­pear­ance, a type de­signer has to har­mo­nize these dis­parate forms.

Our up­per­case al­pha­bet came from the in­scrip­tional cap­i­tals of the Ro­mans. Our low­er­case al­pha­bet came from the Eu­ro­pean un­cial al­pha­bets of the Mid­dle Ages, which them­selves evolved from scribal ap­prox­i­ma­tions of the up­per­case alphabet.

But our fig­ures were in­vented in In­dia. They spread west­ward through the in­flu­ence of Per­sian and Arab math­e­mati­cians. Tra­di­tion­ally they were known as Ara­bic nu­mer­als, but lat­terly as Hindu–Ara­bic nu­mer­als. In­dic and Ara­bic lan­guages, of course, look very dif­fer­ent from Eu­ro­pean lan­guages. Thus, fig­ures have al­ways pre­sented a chal­lenge for type de­sign­ers, as they rely on shapes that are found nowhere in the up­per­case and low­er­case alphabets.

Type de­sign­ers have met this chal­lenge by de­vis­ing sets of al­ter­nate fig­ures, in­tended for dif­fer­ent ty­po­graphic con­texts. Three things to know in advance:

1. It’s never wrong to use the de­fault fig­ures in your font—namely, the ones you get when typ­ing the keys 0–9. Those are put in the de­fault po­si­tion be­cause they’re in­tended to work well across a range of contexts.

2. Not every font has every set of al­ter­nate fig­ures listed here. Al­ter­nate fig­ures are added based on the type de­signer’s im­pres­sion of how the font will be used, and whether the al­ter­nates will be useful.

3. If al­ter­nate fig­ures are in­cluded in your font, they’ll be im­ple­mented as Open­Type fea­tures. Those caveats also ap­ply, es­pe­cially per­tain­ing to ap­pli­ca­tion support.

These are the most com­mon fig­ures. They’re also the ones you’re most likely to find in the de­fault po­si­tion of a font. Lin­ing refers to the fact that fig­ures “line up” at the top and bot­tom. Lin­ing fig­ures can be used in any sit­u­a­tion. Lin­ing fig­ures are al­ways pre­ferred for all caps text be­cause they come clos­est to cap height.

Un­like lin­ing fig­ures, old­style fig­ures are de­signed to look more like low­er­case let­ters. The ones in Eq­uity (shown be­low) are typ­i­cal—some are short, some de­scend be­low the base­line, and some as­cend. You won’t be sur­prised to hear that old­style fig­ures work best in low­er­case body text.

Still, I won’t say that they’re in­her­ently bet­ter than lin­ing fig­ures for that pur­pose. As with jus­ti­fied text, you’ll see it done both ways in pro­fes­sional ty­pog­ra­phy. And in con­text, old­style fig­ures some­times look a lit­tle, well, old. So the choice is yours.

With caps, how­ever, you should not use old­style fig­ures. They look wrong.

Tab­u­lar fig­ures are set on a fixed width. That way, each fig­ure oc­cu­pies the same hor­i­zon­tal space on the page. Pro­por­tional fig­ures are not like­wise uni­form: the fig­ures are set on vary­ing widths that suit the shape of the figure.

Note that whether fig­ures are lin­ing or old­style is sep­a­rate from whether they’re tab­u­lar or pro­por­tional. In fact, some fonts have all four pos­si­ble com­bi­na­tions—lin­ing pro­por­tional, lin­ing tab­u­lar, old­style pro­por­tional, and old­style tabular.

In body text, pro­por­tional fig­ures are pre­ferred be­cause they tend to have more even spac­ing and a more con­sis­tent ap­pear­ance. But tab­u­lar fig­ures are es­sen­tial for one pur­pose: ver­ti­cally aligned columns, like you find in grids of num­bers.

That said, the de­fault fig­ures on many fonts—es­pe­cially sys­tem fonts—are tab­u­lar lin­ing fig­ures, so they can move eas­ily from your word-pro­cess­ing doc­u­ment to your spread­sheet. To check if your font has tab­u­lar fig­ures, type a line of ze­roes above a line of ones. If they’re the same length, then your font has tab­u­lar figures.