# 0 - Constants, Variables and Notation

## 0.1 Important Constants​

ConstantsDescription
10 minutestarget duration of a sub-slot
32 blockstarget number of blocks per sub-slot
16/64 blocksminimum/maximum number of blocks in a slot
4608 blocksaverage number of blocks per epoch
384 blocksaverage number of blocks per sub-epoch
64 signage pointsnumber of signage points per sub-slot

The above imply the following:

Implied ConstantsDescription
1 daytarget time of an epoch is $10 {\ \sf min}\cdot\frac{4608{\ \sf blocks}}{32\ \sf blocks}=1440{\ \sf min}\quad (=1{ \sf day})$
2 hourstarget time of sub-epoch
18.75 secondstarget average block arrival time is $\frac{10{\sf\ min}}{32}=18.75 {\sf\ sec}$
9.375 secondstarget time between signage points is $\frac{600}{64}=9.375 {\sf\ sec}$

## 0.2 Important Variables​

VariableDescription
$D\in{\mathbb N}$difficulty parameter. Re-calibrated once per epoch to meet target of $32$ blocks per slot
$T\in {\mathbb N}$time parameter (number of VDF steps for sub-slot). Re-calibrated once per epoch to meet target of $10$ minutes per sub-slot

## 0.3 Boxes​

Objective 0:

We will use blue boxes like this one to mention key objectives we want the design of Chia to satisfy

Design Choice 0:

Green boxes like this are used to highlight important design choices, which often will refer to objectives.

Security Notice 0:

A red box stresses some important aspects required for the security of Chia, and will typically refer to some design choice.