Inflation is not included for two reasons.
First, because mid and long-term inflation mainly responds to economic growth and labour market developments –two aspects that are already reflected in other indicators.
Inflation is the rise of consumer prices and, as such, stems from the interaction between aggregate demand (e.g. the total demand of households and companies); labour labour market developments (the pace of employment creation and unemployment rate); and the prices of goods imported from abroad (such as oil, gas, utilities and food).
The first two factors (aggregate demand and labour market developments) are mainly domestic. They conform structural features of the economy and thus explain long-term inflation dynamics. Yet, as stated above, these relevant features are already included in other indicators of the compass. By contrast, the third factor (the prices of imports) is far more volatile, since it depends on a number of exogenous variables which are often subject to international shocks (such as wars, climate catastrophes and problems in global supply chains).
The second reason why inflation is not included in our compass is because it's hard to characterize inflation as "good" or "bad" for the economy. Inflation is not intrinsically good or bad as it is, for instance, poverty. In Spain’s recent economic history there have been years of robust economic growth and improved working conditions in which inflation was relatively high. By the same token, there have been periods of sharp falls in inflation that could not be considered positive since such falls were the reflection of an economic crisis (reduced activity and increased unemployment). To sum up: ups and downs in inflation within a long cycle of 40 years or more say little about how well or bad an economy has performed. Thus, it is not used as an indicator in the compass.