Generate calibrated spikes on top of mains

[electricspark]

I recently purchased an old analogue Cole Mains Check Set model T1007 in mint cosmetic condition.  It measures mains voltage and frequency plus four transient levels (10V, 50V, 100V and 200V).  The V & F were a little out so I calibrated them against my Brymen BM867s. But I’m at a loss as to how I can easily and cheaply generate a 10/50/100/200 volt spike on top of standard 240 volt mains so I can check/calibrate the remaining four functions.  I can’t find an info on Google apart from pictures of the T1007. Has anyone got any ideas?   

Thanks!