Blue square on schematics

[Gibek2600]

Hi everyone i have a problem. On some schematics there is large blue square with K numer (5K or so) what is it?
here is link to screenshot http://i.imgur.com/V4R1D4u.png
sorry for poor english

[bluebunny]

Welcome.  That'll be a trimmer (variable resistor that you set once and forget).  Something like one of these:

[antonis]

you set once and forget

For a complete oblivion, a smear of laquer should be very helpful..