Musing on Tilly Units of Measure (TUM) in Tilly’s Very Bad Day

As I think about possible changes for a Tilly’s Very Bad Day 2.1, and continue my design of Deep Battle, I’m revisiting my decision to use Tilly Units of Measure (TUM). Should I have gone with Base Widths instead?


Three factors meant I went for Tilly Units of Measure (TUM) in Tilly’s Very Bad Day.

Firstly, I like rules that use base widths as the unit of measure. I’m not sure why, but it seems more elegant than, for example, inches. Bear in mind I’m from New Zealand and New Zealand has been metric my entire life so rules that use inches always make me go “ah, right, those inch things”.

Secondly, I wanted to use my Big Bases but didn’t want to restrict how other people base their figures. And for Tilly’s Very Bad Day I know people are using anything from 40mm to 120mm for a base width. I don’t care so the rules don’t care.

Lastly, and rather embarrassingly, I have some awkward measurements in Tilly’s Very Bad Day. There is a rule that uses ½ base width and another that uses 1½ base width. In an attempt to dodge that difficulty I decided to standardise on ½ base width for all measurements. I gave this ½ base width a name, TUM, because “½ base width” doesn’t roll off the tongue.

That change means I can say, “infantry move 3 TUM” rather than “infantry move 1½ base widths”

This is what Tilly’s Very Bad Day actually says about TUM:

All distances are relative to the base width of an infantry or cavalry unit. The specific base width you use does not matter, but having a consistent base width does.

The actual unit of measure is one half a base width, called a Tilly Unit of Measure or TUM for short. This is half the base width of an infantry or cavalry unit.

That text is accompanied by a graphic:

Tillys Very Bad Day - Base Width
Tillys Very Bad Day – Base Width

Base Width

Because my 8cm wide Big Bases are different and smaller than the 4-6″ bases of One Hour Wargames, I converted Martin Rapier’s One Hour WW2 (6 hit) to using Base Width measurements.

It was this variant we used for Leshnov 1941 – A Battle Report for OHW 6 Hit. I was right back to “infantry move 1½ base widths”. Initially Chris reacted negatively but then we got on with it and the game played okay.

So now I’m wondering whether introducing TUM made things simpler or more complicated? Given every TUM measurement has a Base Width equivalent, should I have stuck with base widths?

Tillys Very Bad Day - TUM versus Base Width
Tillys Very Bad Day – TUM versus Base Width

Observations and Conclusion

I think base widths are simpler. But fractions of base widths undermine that, hence introducing TUM. But was it really necessary? I don’t know.

What do you think?

Where to get Tilly’s Very Bad Day

Tilly’s Very Bad Day is available for Download (PDF).

13 thoughts on “Musing on Tilly Units of Measure (TUM) in Tilly’s Very Bad Day”

  1. I am struggling with that myself and I have a come to this conclussion: meassure units should not depend on base with but table depth.

    People who use bigger bases use to play in bigger tables. I have been testing for a while and I think Shorter table side/30 is a good value for standar movement. (120 cm depth means 4cm TUM).

    That works for me because I like mini wargaming and play in 60×60 cm tables with 10/6mm miniatures on 4 cm with bases.

    When I want to play bigger battlrs in bigger tables I just addapt the TUM to the new table size and add more troops. Movement keeps proportionally constant and I have just a bunch of more miniatures to play.


    • Exactly. Base size and table size are related and I make that explicit in Tilly’s Very Bad Day.

      Small Table: square, with 30 TUM to a side. With my 80mm wide bases, a square 30 TUM by 30 TUM table is 4’ x 4’ (120cm x 120cm).
      Big Table: 45 TUM by 30 TUM. With my 80mm wide bases I use a 180cm x 120cm (6′ x 4′) table.

      People who want a smaller table (e.g. 2′ x 2′) will use smaller bases. And people using bigger bases should use a bigger table.

  2. I prefer Base Widths because they are an obvious visual amount related to stands, whereas having to think “TUM=half a base width” adds one more level of abstraction/calculation for my addled mind! using your rules I have always interpreted 3 TUM as 1.5 BW before measuring. 🙂

  3. Hi Steven,

    Thoughtful post. My view is that the measurement system in Tilly is fine, though I have two, perhaps quite personal, caveats about it.

    It’s fine because the use of units that are not fixed, like centimetres or inches, but are set relative to the base size that an individual user might want to adopt for their physical model of the game and that is really helpful. It’s also current practice across most of the hobby, which practice has been adopted for mainly for that reason. Tilly is consistent with that even though you’ve adopted a half BW as the unit of measurement.

    Now for the caveat. That decision, to adopt the half BW as the standard, leaves you with the problem of what to call it. BW has become the conventional, familiar usage, following its adoption for DBA V3, but a half BW doesn’t have any convenient, conventional term associated with it. So you’re stuck with inventing a name, which may work for one player but not another. I struggle with TUM for no good reason but I’m sure others don’t.

    My second caveat about utilising the BW as the standard unit of measure AND calling it such, is this.

    When I first played DBA, a long time ago, the unit of measurement was a standard length (an inch, I think) but that equated to 100 paces. All measurements in the game were then described as multiples of 100p. That had one big virtue to me. It helped with the suspension of disbelief that I find to be so much a part of enjoying the game. Thinking of my bows as having a range of 300 paces just feels more real.

    In the early versions of DBA, the 100 pace increments were not so directly related to BWs but in HFG (Horse, Foot and Guns, the black powder equivalent, which I really enjoy playing) measurements are all given in paces and all are multiples of 200p, which is half a BW. So my 6pdr batteries have a range of 1600p. Perfect! That’s satisfying to say, especially when their fire discomfits my enemy, and easy to measure as it’s 8 x 1/2 BW units.

    So that’s the way that I’m going with all my pre-modern rules from now on. 🙂 But Tilly is a great set of rules anyway so I wouldn’t sweat over it.

    Best regards, Chris

    • I’m not a fan of paces as they hurt my head. Just like you and TUM, it is a personal thing. Clearly other folk like them.

      Of course, I used paces in early versions of the WRG rules. And inspired by DBA, I also used paces in my first version of Twilight of the Sun King. I defined the ground scale as “100 paces (p) is 1 cm”.

      I abandoned paces for a couple of reasons, but the primary reason is I get addled brain syndrome anytime a set of rules talks about them. Even if I wrote the rules. How long is a pace? Whose definition of a pace are we using (it differed over time and by location). Luckily, Phil Barker defined his pace somewhere and basically in WRG land 1 pace = 0.75 metres. Having discovered that, any time a set of rules talked about paces, in my head I converted paces to metres. So for Twilight I’d go, right the rules say “100 paces (p) is 1 cm” and what that actually means is 100 x 0.75 = 75 metres is 1 cm, which is 1:7500 ground scale. Try doing that a few times in a game and you’ll realise it is quite exhausting.

      I think in metrics (metres and all that). I can cope when people talk imperial measures (inches, miles, etc) and occasionally do it myself. But paces are beyond me.

      I wrote Tilly’s Very Bad Day partly as a corrective script for Twilight of the Sun King. So I deliberately left out the ground scale. Stating the ground scale in Twilight forced the rules down a game design route that I ended up not liking. I was more interested in fun game play, so I left the number crunching out of Tilly. There is a ground scale and I might post about that soon, but it isn’t essential.

      My 2023 variant of Twilight, Twilight of the Britons, also drops paces and goes with base widths.

  4. Dang, it doesn’t matter how many times I read back my comments there’s always one error! The phrase “and that is really helpful”, in the second paragraph, should say “is really helpful”. Sigh.

  5. Hi Steven,

    We use the same BW as you with 20mm flat miniatures. The TUM concept is good for us because inches are not natural to french people.

    We understand that going to BW insteed of TUM would speed the game ( move and fire range X 2) a little like VnB. If this is true, should be tried to see the effect before changing the rules.

    • The French did a great service to the world with the metric system.

      The only thing holding me back from dropping TUM and going Base Width (BW), are hose awkward 0.5 BW and 1.5 BW measures. I have play tested rounding these particular measurements up (so 0.5 because 1 BW and 1.5 became 2 BW) but the game played wrong.

  6. We’re broadly on the same page. I now always use base widths or half base widths as my increment of measure (i.e. the increment on my measuring stick), just as you and most others do. I just call it 200p or 400p or whatever for the reason I mentioned.

    I don’t concern myself much with the precise definition of the pace (or any other unit in the design), mainly because that’s implying a level of precision about the simulation that’s simply unjustified and detracts from my “suspension of disbelief”.

    On the other hand I do find it very helpful to think of 1200 paces as not far off a kilometre or 2000 paces as not far off a mile because I get a better sense of the overall scale of the game.

    The thing I don’t want to do is use a modern measurement system in a game that can’t readily be related to it. I’d much rather use an arbitrary increment like a TUM, so Tilly certainly does it for me. Most of the sources, if they mention a unit of measurement at all, talk very generally, often using terms like “bowshot” or “musket shot” or, occasionally, “paces”.

    All the best, Chris

  7. I personally prefer TUM, precisely because of the awkwardness of 1.5 BW. Also, I agree with Antonio that it would probably be better to tie the measure to the size of the table.

    For example, I am used to playing on 120×120 or 180×120 centimetre boards. This means that since small battles should be played on a 30×30 TUM table, one TUM in my case equals 4 centimetres, which in turn dictates the use of 8 centimetre wide bases.

    Then, when I teach the rules to my fellow wargamers, I simply change the TUM distances to multiples of 4cm – for example, cavalry moves 24cm. And then we just play with the tape measure. So in the end it doesn’t really matter whether it’s defined in TUM or BW, we still come up with a distance in metric and use it.

    • Yay, a fan of TUM. And a 8cm big base user.

      As I said above, the TUM is explicitly tied to the table size. What you describe is embedded in the rules.


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