Orange Jelly, Orange and Lemon or Grapefruit Jelly

This is one entry in a Certo pamphlet where a single master method served a whole page of fruits, so the text breaks off at "proceed as below." What follows fills in the gaps and translates the units.

• The missing methodThe standard liquid-pectin procedure: measure the prepared juice into a large deep pan, add the sugar, mix, bring to a hard rolling boil over high heat, add the Certo all at once, bring back to a full boil and boil hard for the short interval the pamphlet's master directions specified — period Certo jelly directions generally called for half a minute, later and modern liquid-pectin directions for a full minute — then remove from heat, skim the foam and pour into hot sterilized jars.
• "13½ lbs." is a misprint"13½ lbs." cannot be right -- Three cups of juice weighs about 1½ lb, not 13½, and 7 level cups of sugar does come to roughly 3 lb. Read the first figure as 1½ lb; the parenthetical weights appear to be offered as an alternative to measuring by volume.
• One bottle of CertoThe recipe glosses the bottle as a "scant cup," i.e. close to 8 fl oz; bottle sizes changed over the product's life, so measure rather than assume. Liquid pectin is now sold in 3 fl oz foil pouches, so match the volume the recipe asks for. Powdered pectin is not interchangeable — it is added to the fruit before the sugar, not after.
• Getting three cups of juiceTwelve oranges will give roughly 3 cups once crushed and strained; grapefruit varies enough that you should measure rather than count. Crush the segments, then drip through a damp jelly bag or several layers of cheesecloth without squeezing if you want a clear jelly.
• Why the lemons are offeredSweet oranges are relatively low in acid, and liquid pectin needs acid as well as sugar to set, so the ten-oranges-and-two-lemons version is the safer bet of the two orange options; with all oranges, add the juice of a lemon as insurance.
• The grated rindTake only the colored zest and none of the white pith, which is where the bitterness sits. The grapefruit instruction to remove the white rind "in quarters" most likely means scoring the peel into four sections and peeling it away before crushing the segments.
• Do not lengthen the boilThe short boil after the pectin goes in is the whole mechanism. Boiling on well past it degrades the pectin and can leave you with a syrup that will not set properly, the opposite of the long-boil habit these pamphlets were written to replace.
• SealingThe original assumed a layer of melted paraffin over the surface. That is no longer considered a sound seal; use two-piece canning lids and a ten-minute boiling-water bath, or refrigerate the jars and use within a few weeks.
• YieldAbout 8 cups of finished jelly, or roughly eight half-pint jars; period pamphlets for this quantity quote about eleven six-ounce glasses.