A Reddit post schooled Sydney commuters on what a series of numbers seen near train tracks actually mean.
It was initially intended to be information for those who usually enjoy a nap on their commute, but it was a lesson for just about anyone who catches a train in Sydney.
The Reddit user, MrSmithSmith shared a picture of a pylon near the train tracks. On the pole is a yellow sticker with a series of digits "N44+641".
It's likely you've seen something similar when looking out the train window in Sydney, but judging by the comments, it seems not many people knew what the letter and numbers meant, or took much notice.
"All overhead wiring structures on the network have a pylon number which tells you the exact distance to Central," MrSmithSmith wrote on Reddit.
"In this example, we're on the [N]orthern line, 44.641km from Central Station."
The letter at the beginning indicates the line you are on and the numbers signify the distance, with the plus sign representing a decimal point.
Yahoo News Australia confirmed with Sydney Trains the number does represent the distance from that point to Central Station.
"A lifelong mystery... solved," someone said in the comments of the Reddit post, thanking MrSmithSmith.
Someone also noted the picture looked as though it was taken at Berowra in northern Sydney, which MrSmithSmith confirmed is correct.
Another person shared a picture of the reference marker at Central Station, which is between platforms 1 and 2 and the marker reads "B0+000".
On the Reddit post, MrSmithSmith linked to a list of abbreviations used for the train lines and "B" signifies the Bankstown line.
A few pointed out the markers were used by maintenance staff but MrSmithSmith had a few other suggestions on what they could be used for — like those who want to play a "guess the next number" while on a commute.
Someone else pointed out they could be used if you're on a train and there is an incident to tell someone exactly where you are on the tracks.
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