Alright... now that I'm sure that eKLaB is familiar... or at least "informed" of the negative effects Methamphetamine/Amphetamines can have on the mind/soul at work, I'm not going to tell him to, "not do it".
...But if you ARE going to take Amphetamines/Methamphetamines at work, I highly reccomend you being cautious of the way you're going to feel after it takes it's toll, or are aware of the fact that you may very-well be experiencing dehydrative effects from using this substance.
Just be sure to consume enough water (this all depends on dosage, but I would generally say roughly about 300ml-500ml/hour of water.
Also... be sure that there is a posibility of you "wigging out" at work, in front of other people, raising their suspicions of you coming to work under the influence of an intoxicative substance.
If you don't go over-board, you should be alright though... yet, I still don't reccomend tweaking before work-hours, it would be a more enjoyable experience after work at a club or something.
As for dosing yourself, it all depends on your sensitivity to the drug, but if you're an in-frequent user of Methamphetamine (this is judging by the gear I get my hands on anyways...) you shouldn't really have any more than half a point-to 1 point of it before work.
I'd say half a point should be a sufficient amount to get mentally and physically stimulated to the degree of it "enhancing" your work perfomance (me saying this, in NO WAY means it WILL effect YOUR performance in a positive way however.)
Just be careful man. Make sure you are familiar with the products potency before using it for work.
Be absolutely sure that you want to do this... make sure other people's lives aren't at risk whilst under the influence of the substance (no matter what you do for a living).
Try and eat some solids on your lunch break as well. It may be hard "downing" the food at the time, but it will increase your chances of not feeling so shitfull once the come-down kicks in.
I shouldn't have to remind you about the water(?).
Good-luck with the trial... and let this not be a job to support an on-coming addiction to an (when abused in excess) extremely debilitating chemical/substance.