Date arithmetic

[Marcin Owsiany]

Hello,

I'm trying to use ledger (among other things) to keep track of when my bank deposits end.

Example transaction:

2019-12-05 ! x
  Deposit  7 EUR
  ; duration:: 30d
  Cash

This seems to work as expected:

ledger -f t.ledger --limit "account =~ /Deposit/" --format "date:          %(format_date(date))\ndate+duration: %(format_date(date + tag('duration')))" register
date:          19-Dec-05
date+duration: 20-Jan-04

But changing the duration to 1 month yields strange results:

2019-12-05 ! x
  Deposit  7 EUR
  ; duration:: 1m
  Cash

ledger -f t.ledger --limit "account =~ /Deposit/" --format "date:          %(format_date(date))\ndate+duration: %(format_date(date + tag('duration')))" register
date:          19-Dec-05

date+duration: 20-Feb-03

What's going on? Is 1m not what I think it is?

I failed to find how duration values are parsed in documentation and in source code. Can someone please point me at the relevant place in either?

Marcin