pymetrics Tower Game: Tower of London Rules Explained

The pymetrics Tower game asks you to rearrange coloured discs on three pegs until your towers match a target, in as few moves as you can. Prep sites often call it the Hanoi game, but it is a version of the Tower of London, a planning task with different rules. It is one of the 12 core pymetrics games, which Harver now runs as its gamified assessments after buying pymetrics in August 2022. Prep sites usually report it as the eleventh game.

Facts below are labelled official (pymetrics or Harver material, including pymetrics' patent), prep sites (commercial descriptions) or not public.

The Tower game at a glance

	What is known	Source
Task	Rearrange five coloured discs on three pegs to match a target, within a time limit and in the fewest moves	Official (pymetrics patent)
What is recorded	The number of moves and the thinking time before your first move	Official (patent)
Screen	A target panel above your three towers, Undo and Clear buttons, a 2:00 timer	Prep-site simulation
Controls	Click the peg to take from, then the peg to drop on	One prep site
Number of puzzles	Not published	Not public

What you see and do

Instructions. Read them in full; your version may differ from prep-site reports.
The target and your towers (prep sites). A simulation shows a "Target Towers" panel at the top and your three pegs below it.
Move one disc at a time (official). Only the top disc of a peg can move. The discs are all the same size, so any disc can sit on any other (our reading of the patent; prep sites that add a size rule are mixing it up with Hanoi).
Undo or clear (prep sites). Buttons let you take back a move or start the puzzle again. How the real game counts those moves is not public.
Finish or run out of time (prep sites). One simulation shows a 2:00 timer. Whether the real game has one puzzle or several is not public.

The psychology behind it: the Tower of London

Tim Shallice (1982) designed the Tower of London to study planning in people with damage to the frontal lobes. In his version, three coloured beads sit on three pegs of different lengths, and you move them one at a time to reach a goal arrangement in a set number of moves. It became a standard test of planning ahead.

It is often confused with the Tower of Hanoi, which uses discs of different sizes, forbids putting a larger disc on a smaller one and asks you to move a whole stack. The Tower of London has no size rule; the challenge is working out the order of moves before you start. pymetrics' three pegs and five same-size coloured discs follow the London design.

What it is thought to measure

pymetrics' patent says the game records how many moves you make and how long you think before your first move: two classic planning measures. pymetrics does not publish how it weighs them, for example whether a long first think counts for or against you in a given role.

Overall, pymetrics compares your play across all the games with people who do well in the role and gives the employer a fit score, not a pass mark (official). See pymetrics results and the trait report.

Is there a right answer?

Partly. Each puzzle has a fewest-moves solution, and often more than one route reaches it, so how close you get can be measured. But there is no published target for moves or thinking time, and pymetrics says there is "no right or wrong answer" across its games: your whole profile is compared with people in the role. More in pymetrics games answers.

Timing and length

The whole set (official): about 25 minutes for the 12 games, 1 to 3 minutes each, with no pausing mid-game.
Tower (prep sites): one simulation shows a 2:00 timer. The number of puzzles is not public.

How to approach it

pymetrics' advice is to be yourself. In Tower, that means planning the way you naturally would, with full attention.

Study the target first. Look at it before you touch a disc.
Work from the bottom up. Find which disc must end at the bottom of each target peg and clear the way for it.
Use the emptiest peg as a parking space for discs that are in the way.
Think as long as you need, then move steadily. The patent records thinking time, but no source says what is good, so there is no point rushing or stalling on purpose.
Use a computer if you can. Prep sites advise one; clicking pegs is easier with a mouse or trackpad.

Common mistakes

Applying the Tower of Hanoi rule and refusing to put one disc on another.
Moving straight away, then undoing and redoing moves.
Parking a disc on top of one you need next.
Treating Clear as a free restart: whether earlier moves still count is not public.

A worked example

A small puzzle we made up. Pegs are listed bottom to top.

Start: peg 1 holds red, blue, green; peg 2 holds yellow, purple; peg 3 is empty.
Target: peg 1 holds red, green; peg 2 holds yellow, purple, blue; peg 3 is empty.

Fewest moves (3):

Green from peg 1 to peg 3, to park it.
Blue from peg 1 to peg 2.
Green from peg 3 back to peg 1.

A tempting route (4 moves): green goes to peg 2 first. It now sits on purple, exactly where blue needs to go, so blue has to park on peg 3, green moves back to peg 1 and blue finally moves to peg 2. A few seconds spent checking where blue had to end up would have shown that peg 3 was the right parking spot.

How Candidate Falcon's Tower practice works

Candidate Falcon's independent pymetrics Tower practice game uses the Tower of London rules with original screens. It is not the real game.

5 puzzles per run, needing 3, 4, 5, 6 and 7 moves at the fewest, generated fresh each time; every minimum is checked by searching all possible arrangements.
Five same-size coloured discs on three pegs. Tap a peg to pick up its top disc and another to drop it, or use keys 1 to 3.
2:00 per puzzle, with the fewest possible moves shown on screen.
Undo and Clear all, but every move you make still counts.
A review of your planning time, your moves against the fewest possible and a shortest solution for each puzzle.

The 5 puzzles, the on-screen minimum and the move counting are our choices. Practice results are not pymetrics or Harver scores. The pymetrics games come with every plan that includes Harver; see pricing. The free pymetrics guide covers the whole battery.

FAQs

Is the pymetrics Tower game the Tower of Hanoi?

No. It is a Tower of London task. The discs are all one size, so there is no rule about which disc sits on which. You move only the top disc of a peg to copy a target.

What does the pymetrics Tower game measure?

pymetrics' patent says it records the number of moves and the thinking time before the first move, both linked to planning. pymetrics does not publish how it scores them.

How many puzzles are in the pymetrics Tower game?

That is not public, and prep sites leave it unresolved.

Is the Tower game timed?

The patent mentions a time limit, and one prep-site simulation shows a 2:00 timer. Each pymetrics game lasts about 1 to 3 minutes in total.

Sources

pymetrics patent WO2015200880A1: pegs, discs, target, time limit, moves and thinking time.
Wilson et al. (2021), Building and Auditing Fair Algorithms, with pymetrics co-authors: devices, the fit model.
pymetrics candidate FAQ, employer-hosted copy (2018): timing, no pausing, no right or wrong answer.
Harver: gamified assessments and Harver acquires pymetrics (read October 2026).
Prep-site descriptions (a JobTestPrep simulation and others): screen, buttons, timer, controls.
Shallice, T. (1982). Specific impairments of planning. Philosophical Transactions of the Royal Society of London B, 298(1089), 199–209.

Candidate Falcon is independent and not affiliated with pymetrics, Harver or any employer.