OK, please don't flame me because I'm using a digital camera to test my light meter. I recently purchased a Sekonic L-508 off ebay. Once I got it I realized I had no idea if it was accurate or not. I've never used a light meter before. I bought it to use with my three Pentax SLRs. So I sent it to Quality Light Metric Co. which I've read is very good. He said he did make some adjustments and brought it within factory specs. He said he calibrated it at 18% gray.

So I'm testing it out tonight. The incident meter seems to land pretty regularly around 18%, judging from my histogram (pentax k-5). The graph stacks up just left or directly on the mid-line.

The spot meter (1 to 4 degree) OTOH is a different story. I played with it outside, pointing at all kinds of things and the result was always a blown out picture. I came inside and spot metered off of a gray card on the wall. The Sekonic gave me a reading of 1/30th, f/2.4 @ 1600 ISO. The incident meter just in front of the card gave me a reading of 1/500, f/2.4 @ 1600 ISO. The incident meter was right within that 18% range. The spot was of course overexposed.

Is this typical of a spot meter to be that much off? I can dial in a compensation from -9.9 to 9.9, to "calibrate" the spot meter. I know the spot and incident typically read differently, but 4 stops seems like a lot different. So should I send this back to Quality Light Metric or not? If I shouldn't, what compensation should I dial in on the spot meter?

Sorry this was so long but I'm confused.
Thanks,