Sorry you have become confused, it's undersandable. If you want a short answer to your question "Do I really need a light meter?" then the answer is No! When you get fed up of taking your camera of the tripod to to take a close up reading or otherwise feel the need to buy one, that's the time to spend your hard earned money.

For xmas I was given some jessops vouchers and I've exchanged the for various gadgets. One being a grey card to check grey balance and exposure levels. This morning I'd spotted a few Iris had flowered in the garden. The light was very soft, dull, misty and overcast this morning normally ideal for flower shots. I decided to have a play with the grey card mainly to correct for colour shifts at the post processing stage. At the same time I thought it would be interesting to see what exposure readings I get with it.

With the camera set in manual mode the camera's matrix reading was 1/3 Sec f13 ISO100 of the scene. From the grey card it was 1/10 Sec f13 ISO100.

Attached are the 2 shots straight from the camera, cropped only and pasted together. The darker side has the grey card included for checking the colour balance. Assuming that if the grey card is correctly exposed it should be a mid grey on the final image. The second image shows the grey card version adjusted to give a mid grey and a slight contrast boost.

So am I correct in assuming the grey card should read level 127 in PS when exposed correctly ? To me the adjusted looks a bit on the dark side but that maybe my monitor setup.

Yes Rob you are correct in expecting the grey card on the monitor to read 127 for R,G & B providing the white balance was set correctly on both camera and monitor. I would expect the matrix reading to be a longer exposure than that indicated by the grey card because of the dark background. One and three quarter stops though is a bit of a surprise.