Now and then I like to try to solve a puzzle

with just a pen, without marking any candidates.

I just use these 2 techniques repeatedly:

1) Look at a single row (or column or block).

Check for all the cells where a 1 could go.

If there is just 1 such cell, then enter the 1 there.

Repeat this for digits 2-9 (except of course for

the digits that already appear in the group).

2) Choose one blank cell. Consider all the values

that could still be entered in that cell (based

on other values already entered in that cell's

column, row, and block). If there is only 1 value

that can still legally be entered there, then

enter that value.

These techniques are just the obvious ones,

and they are not very powerful (equivalent

to checking for hidden and naked singles with

candidates).

So I wonder: are there other techniques I could use?

(Preferably without too much brainpower required .... )