A recap of some of the fundamental parts of a circle, including some that are easy to forget:

Diameter — a line crossing the circle through its centre. Also the longest straight line you can draw in a circle.

Radius — a line from the centre to any point on the edge. Also, half the diameter.

Sector — the classic Trivial Pursuit cheese, pizza or cake slice formed by two radii.

Area — equal to pi x the radius squared.

Circumference — equal to pi x the diameter.

Chord — a straight line touching any two points of a circle. The longest chord is the diameter.

Segment — the areas on either side of a chord, major and minor.

Tangent — a straight line just touching the edge of the circle without crossing it. It forms a right angle to the radius on the edge. Just as if you were able to lean a ladder against one.

More maths and science refreshers: States of matter, BODMAS (or PEMDAS), the 9 times table on your fingers, binary, incidence and reflection

Parts of a circle

Metrics are like an onion: full of layers.

A simple question to ask can often be complicated to answer. Or we may find that we need to ask a different question. While it'd be lovely to have one simple metric to understand our business the reality is usually a lot more nuanced and interesting than it first seems.

Averages will deceive. Vanity metrics may wow —  by, say, quoting a total user count and conveniently ignoring whether those users are actually paid, active, or leaving. Growth overall can hide declines in other areas or product lines and vice versa. The people on monthly subscriptions may be doing great, while revenue from add-ons may be declining. New users may be signing up in droves while existing users are churning. Mobile traffic may be different from desktop, online sales different from store sales... In practice, it's the hard questions we're usually asking even if we don't know how to ask them.

It pays to carefully consider what you're trying to learn and to understand all aspects of a business before putting faith in the numbers. And it may make sense to start with simpler metrics first.

The metrics onion

When you're deep in, it may feel like you have no time to pause. No time to take a break, there's too much to get done. Perhaps no time to stop and think about how you're working. No time to step back and improve your processes or work on your tools. Maybe even no time to look after yourself, to recharge, to reflect, to take a walk.

As the metaphor goes, you may feel you have no time to stop and sharpen the saw. Until you do it, and then you may realise you have no time to not stop and sharpen the saw.

Sharpen the saw is habit 7 of Steven Covey's classic The 7 Habits of Highly Effective People