Please be aware that on page 271 of the print version, and the old Hypokalaemia page (now corrected) (Link) had a few annoying little errors.

ECG changes of hypokalaemia occur when the K+ is < 2.7mmo/L not when it is >2.7mmol/L

The ECG image was of hypokalaemia (as in the title) despite the text beneath stating it was of hyperkalaemia.

U waves are often mistaken as T waves.