The passes are the whole trap
A pattern sheet reads like a table of boards and loads, and it is tempting to add the loads up and multiply once. The load column is per board per pass, so a leg covering 39 boards at 55 microlitres is 2,145 microlitres if the head crosses once and 4,290 if it crosses twice. Five legs at mixed pass counts is five separate multiplications, and dropping any one of them changes the answer by thousands of microlitres.
The default in the form comes to 20,615 microlitres on the boards — 10,490 forward and 10,125 reverse — which is 20.6 mL. Ignore the pass column entirely and the same five legs total 8,620 microlitres, which is 42 percent of the real figure. That is the size of the mistake.
Board-feet crossed is not the same as lane area
The page reports board-feet the head crosses, and that figure counts an overlapped board once for every pass over it. The five default legs come to 12,120 board-feet crossed, giving 1.701 microlitres of oil per board-foot crossed. It is a useful number for comparing two patterns that use the same machine, and a misleading one if you read it as a film thickness, because the boards under the middle of the pattern are crossed several times and the ones out by the gutter once or not at all.
What leaves the tank against what lands
The buffer and the transfer path hold conditioner that leaves the tank and never reaches a board. The default puts 2 mL there, so a lane draws 22.615 mL from the tank to lay 20.615 mL on the surface. If you are ordering drums, the tank figure is the one that matters; if you are talking about the pattern, the board figure is. Two mL a lane across 24 lanes every day for a year is 17.6 litres, which is a drum and a half nobody counted.
Where to get the numbers
The boards, distances, loads and passes come off the pattern sheet your own sanctioning body publishes, or straight off the lane machine display if it reports its own loads. The price comes off the invoice divided by the litres in the drum. None of it is asserted here, and this page makes no claim about whether a pattern meets any standard — it adds up what you tell it.
Questions people ask
Is a load in microlitres per board applied once or once per pass?
Per pass, which is why the form asks for the pass count separately. A leg listed at 55 microlitres per board over 39 boards puts down 2,145 microlitres on one crossing and 4,290 on two. If your sheet quotes a leg total instead of a per-pass load, enter 1 in the passes column and put the total load in.
Why does the total not match the figure printed on my pattern sheet?
Common reasons: the sheet quotes what leaves the tank rather than what lands on the boards, it counts a conditioning pass you have not entered, or the machine trims the load at the ends of its travel. The gap is worth finding rather than fudging — this page adds up exactly the legs you type and nothing else.
Does this tell me whether my pattern is legal for league or tournament play?
No, and it will not. Whether a pattern is acceptable for any given competition is decided by the body that sanctions the house, from their own published rules and their own measurement. This page does arithmetic on numbers you supply.
What about the oil that ends up on the balls?
Not modelled, because there is no honest way to guess it from a pattern sheet. Carry-down and pick-up depend on ball surface, rev rate, how many games have been bowled and where people are playing. The total here is the instruction given to the machine, not the state of the lane an hour later.