well first things first - had it on the WRONG cable
- the negative not the live - well once i had figured out which was the RIGHT one ( why don't they wrap a bit of red tape round the bloody thing to identify it ?? jeez is that TOO much to ask ?? or do they think we all bleeding psychic ?? ) - i noticed that if i moved the sensor the reading varied ( the sensor is quite loose on my cables - sooooooooo i cut a small section of plastic cable covering from some old wire and taped it to the mains lead - the sensor now fits snugly and does not alter the reading if wiggled
- then i fitted the other sensor to the same cable a few inches away - result A; the monitors are reading i assume accurately - well they should be as i turned everything off bar one 400 halogen fire ( which uses 387 w in reality ) -AND B: they now agree within about 30 w of each other - which i suppose aint bad given the verities of manufacturing / differing models etc so you may want to check that your monitor is not doing the same thing ?? - turn everything off bar a KNOWN load eg a 1 kw fire ( having one of those plug in power monitor thingies helps as there is usually a W setting which will tell you pretty accurately the load ) and see if the main monitor reads true ( or near enough for jazz )
if so REJOICE
-if not time to do some investigating 
usual cautions : if you don't know whats what in the meter cupboard call some one who does ( i do and STILL made a mistake- my error - rushing when i fitted it ) ) - and of course don't interfere with anything else in there as electricity is dangerous etc etc - never poke around with metal tools etc or remove covers - and if any thing looks wrong like bare wires ( mice and rats love the plastic ) - call your supplier immediately - blah blah blah - oh come on folks this is common dog
nooooooow what WILL be interesting is if the NEW new monitor i am going to get from British gas as part of their "energy smart " scheme - reads any thing like the same - well if all else fails i can average out the results eh ??
one things for sure i got to cut back some where
- though where i don't know ?? - have already tuned ff those stupid electric brick heaters - so that will save a bit - ho hum - guess a visit to primark ( hush my mouth ) is in order to buy some more fleeces and long johns 
