Simple way to deal with decimals: ignore them, then put appropriate number of dec places in the answer. e.g.
698.12 * 12.4 must have 3 decimal places, so find 69812 * 124 and divide by 1000.
Inequalities are reversed when both sides are multiplied by a ve number. e.g. 5/2 > 2 multiplying by 1 gives 5/2 < 2

This is Nigel's calculator. You can't quite tell the size
from the image, but it's actually really big. Some would call it
archaic, fit only for the partially sighted to convert the time to 24
hour notation. However its simplicity is appropriate to Nigel's desire
to do everything in the cleanest, most elegant fashion. This approach
usually takes ten times longer than the easy way though, much to the
chagrin of his colleagues.
Nigel also has a horrible Texas Instruments calculator.

Nigel often draws diagrams to illustrate his point. If
this fails to work he throws stationary until the line of reasoning is
established. 

Some details of Nigel's life far funnier than this are found on Blinman.com
